<script>
function FormatNumber(num,dec) {
dec= (dec)?dec:2;
ee = Math.pow(10,dec);
nn = Math.floor(num*ee);
vv = String(nn/ee);
vv += (vv.indexOf(".")>=0)?"":".";
while (vv.indexOf(".")>vv.length-dec-1) { vv += "0" }
return vv;
}
</script>

<input type=text onblur="this.value=FormatNumber(this.value,2);">