<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
<script type="text/javascript">
function calculate(){
var valsel = $('[name="select7"] option:selected').val();

if(valsel != "Non U.S."){
var valone = 1.04;
var feeper = .04;
}
else {var valone = 1.05;
var feeper = .05;
}
var valtwo = $('#item2_number_1').val();

if(valtwo!=""){

var fee = valtwo * feeper;
var value = parseFloat(fee).toFixed(2);
$('#item3_number_1').val(value);
var fee = valtwo * valone;
var total = parseFloat(fee).toFixed(2);
$('#item5_number_1').val(total);

}
}
</script>

$('select[name="mydropdown"]').val()

$('input[name="total"]').val()

$('input[name="quantity"]').on('keyup', function() {
var amount = $(this).val() * 10;
if(amount > 0){

$('input[name="total"]').val(amount);
$('input[name="total"]').addClass( "sum" );
calc_total();
}
});

function calc_total() {
var sum_total = 0;
$('.sum').each(function(){
sum_total += parseFloat(this.value);
$('input[name="grand_total"]').val(sum_total);
});
}