beh... prova

function prezzoTot(){
tot=0;idd='';
for(i=1;i<4;i++){
currLine=0;
if(document[formName].elements["campoH"+i].value!='') currLine=document[formName].elements["campoH"+i].value;
tot+=parseFloat(currLine);
}
num = Math.round(tot*100)/100;
str=""+num;
if(str.indexOf(".")<0) str=str+".00";
if(str.length-str.indexOf(".")==2) str=str+"0";
document.getElementById("prezzoTot").innerHTML = '€ '+str;
}