Solo numeros con 1 punto y maximo dos decimales

filterTwoDecimalsInInputTextJS.html

<script type="text/javascript">
<!--
function filterFloat(evt,input){
    // Backspace = 8, Enter = 13, ‘0′ = 48, ‘9′ = 57, ‘.’ = 46, ‘-’ = 43
    var key = window.Event ? evt.which : evt.keyCode;    
    var chark = String.fromCharCode(key);
    var tempValue = input.value+chark;
    if(key >= 48 && key <= 57){
        if(filter(tempValue)=== false){
            return false;
        }else{       
            return true;
        }
    }else{
          if(key == 8 || key == 13 || key == 0) {     
              return true;              
          }else if(key == 46){
                if(filter(tempValue)=== false){
                    return false;
                }else{       
                    return true;
                }
          }else{
              return false;
          }
    }
}
function filter(__val__){
    var preg = /^([0-9]+\.?[0-9]{0,2})$/; 
    if(preg.test(__val__) === true){
        return true;
    }else{
       return false;
    }
    
}
-->
</script>
<input type="text" name="moneda nac" id="moneda_nac" value="10" onkeypress="return filterFloat(event,this);"/>