ako spraviť dynamický podmienený súčet - amatér

<form name="polozky" id="polozky">
<table cellpadding="0" cellspacing="0">
    <tr>
       <td>Názov položky</td>
       <td>Predajná<br>cena v €</td>
       <td>Množstvo</td>
       <td>MJ</td>
       <td>€ spolu<br>bez dane</td>
       <td>%DPH</td>
    </tr>
     <tr>
       <td><input type="text" id="nazovPolozky1" name="nazovPolozky1" size="50" maxlength="50" value="<?php echo $nazovPolozky1;?>" /></td>
       <td><input type="text" id="jednotkovaCena1" name="jednotkovaCena1" size="10" maxlength="10" onBlur="addTotals()" value="<?php echo $jednotkovaCena1;?>" /></td>
       <td><input type="text" id="mnozstvo1" name="mnozstvo1" size="5" maxlength="5" onBlur="addTotals()" value="<?php echo $mnozstvo1;?>" /></td>
       <td>
           <select id="mj" name="mj" size=1>
        <option <?php if ($mj == "1") echo "selected"; ?> value="Ks" selected="selected"> Ks</option>
        <option <?php if ($mj == "2") echo "selected"; ?> value="L" > L</option>
        <option <?php if ($mj == "2") echo "selected"; ?> value="Kg" > Kg</option>
              </select>
       </td>
       <td><input type="text" id="cenaSpolu1" name="cenaSpolu1" size="8" value=<?php printf ('%01.2f', round($mnozstvo1 * $jednotkovaCena1,2));?> disabled/></td>
       <td>
        <select id="sadzba_dph" name="sadzba_dph" size=1>
        <option <?php if ($sadzba_dph == "1") echo "selected"; ?> value=" " selected="selected"> </option>
        <option <?php if ($sadzba_dph == "1") echo "selected"; ?> value="20"> 20</option>
        <option <?php if ($sadzba_dph == "2") echo "selected"; ?> value="10"> 10</option>
        <option <?php if ($sadzba_dph == "2") echo "selected"; ?> value="0"> 0</option>
              </select>
       </td>
    </tr>
<tr>
       <td><input type="text" id="nazovPolozky2" name="nazovPolozky2" size="50" maxlength="50" onChange="cisloPolozky();"value="<?php echo $nazovPolozky2;?>" /></td>
       <td><input type="text" id="jednotkovaCena2" name="jednotkovaCena2" size="10" maxlength="10" onBlur="addTotals()" value="<?php echo $jednotkovaCena2;?>" /></td>
       <td><input type="text" id="mnozstvo2" name="mnozstvo2" size="5" maxlength="5" onBlur="addTotals()" value="<?php echo $mnozstvo2;?>"  /></td>
       <td>
           <select id="mj" name="mj" size=1>
        <option <?php if ($mj == "1") echo "selected"; ?> value="Ks" selected="selected"> Ks</option>
        <option <?php if ($mj == "2") echo "selected"; ?> value="L" > L</option>
        <option <?php if ($mj == "2") echo "selected"; ?> value="Kg" > Kg</option>
              </select>
       </td>
       <td><input type="text" id="cenaSpolu2" name="cenaSpolu2" size="8" value=<?php printf ('%01.2f', round($mnozstvo2 * $jednotkovaCena2,2));?> disabled/></td>
       <td>
        <select id="sadzba_dph" name="sadzba_dph" size=1>
        <option <?php if ($sadzba_dph == "1") echo "selected"; ?> value=" " selected="selected"> </option>
        <option <?php if ($sadzba_dph == "1") echo "selected"; ?> value="20"> 20</option>
        <option <?php if ($sadzba_dph == "2") echo "selected"; ?> value="10"> 10</option>
        <option <?php if ($sadzba_dph == "2") echo "selected"; ?> value="0"> 0</option>
              </select>
       </td>
    </tr>
</table>
</form>

<form name="suhrn">
<table cellpadding="0" cellspacing="0">
    <tr>
       <td colspan="2">Celková suma bez DPH</td>
       <td colspan="2"><input type="text" id="cena_celkom" name="cena_celkom" size="15" maxlength="15" value="<?php echo $cena_celkom;?>" disabled/></td>
    </tr>
     <tr>
       <td>VZ 20 %</td>
       <td><input type="text" id="vz_20" name="vz_20" size="10" maxlength="10" value="<?php echo $vz_20;?>" /></td>
       <td>DPH 20 %</td>
       <td><input type="text" id="dph_20" name="dph_20" size="10" maxlength="10" value="<?php echo $dph_20;?>" /></td>
    </tr>
    <tr>
       <td>VZ 10 %</td>
       <td><input type="text" id="vz_10" name="vz_10" size="10" maxlength="10" value="<?php echo $vz_10;?>" /></td>
       <td>DPH 10 %</td>
       <td><input type="text" id="dph_10" name="dph_10" size="10" maxlength="10" value="<?php echo $dph_10;?>" /></td>
    </tr>
    <tr>
       <td>VZ 0 %</td>
       <td><input type="text" id="vz_0" name="vz_0" size="10" maxlength="10" value="<?php echo $vz_0;?>" /></td>
       <td>DPH 0 %</td>
       <td><input type="text" id="dph_0" name="dph_0" size="10" maxlength="10" value="<?php echo $dph_0;?>" /></td>
    </tr>
    <tr>
       <td colspan="2">Centové vyrovnanie</td>
       <td colspan="2"><input type="text" id="centy" name="centy" size="10" maxlength="10" value="<?php echo $centy;?>" /></td>
    </tr>
    <tr>
       <td colspan="2">Fa čiastka v €</td>
       <td colspan="2"><input type="text" id="fa_celkom" name="fa_celkom" size="10" maxlength="10" value="<?php echo $fa_celkom;?>" /></td>
    </tr>
    <tr>
       <td colspan="2">Záloha v €</td>
       <td colspan="2"><input type="text" id="zaloha" name="zaloha" size="10" maxlength="10" value="<?php echo $zaloha;?>" /></td>
    </tr>
    <tr>
       <td colspan="2">K úhrade</td>
       <td colspan="2"><input type="text" id="uhrada" name="uhrada" size="10" maxlength="10" value="<?php echo $uhrada;?>" /></td>
    </tr>
    </table>
    </form>


JAVASKRIPT

<script language="javascript">
function addTotals()
{
with (document.forms[0])
{
var celkomRiadok1=0;
var celkomRiadok2=0;

var fakturaCelkom=0;

celkomRiadok1 = Number(jednotkovaCena1.value) * Number(mnozstvo1.value);
cenaSpolu1.value = parseFloat(Math.round(celkomRiadok1*100)/100);

celkomRiadok2 = Number(jednotkovaCena2.value) * Number(mnozstvo2.value);
cenaSpolu2.value = parseFloat(Math.round(celkomRiadok2*100)/100);

fakturaCelkom = Number(cenaSpolu1.value) + Number(cenaSpolu2.value);
cena_celkom.value = parseFloat(Math.round(fakturaCelkom*100)/100);
}
}
</script>