autmatically add input values as entered

I'm creating a deposit form

I just completed getting it setup to add a new row.  Now I'd like it to auto-sum the input fields.  I won't know a set number of how many fields there will be as the user can add rows as necessary.

Another hiccup is that I am using another function in the field to auto populate a dollar sign as well as the comma and period necessary to confirm the amount.

function formatCurrency(num) {
	num = num.toString().replace(/\$|\,/g,'');
	if(isNaN(num))
	  num = "0";
	sign = (num == (num = Math.abs(num)));
	num = Math.floor(num*100+0.50000000001);
	cents = num%100;
	num = Math.floor(num/100).toString();
	if(cents<10)
	cents = "0" + cents;
	for (var i = 0; i < Math.floor((num.length-(1+i))/3); i++)
	num = num.substring(0,num.length-(4*i+3))+','+
	num.substring(num.length-(4*i+3));
	if (num =="0") {
		return(" ");
	} else {
	return (((sign)?'':'-') + '$' + num + '.' + cents);
	}
  }

Select allOpen in new window

Here is the code I found to add the fields, but it only does it when a button is clicked.  It also can't handle the function formatCurrency() as shown above.

$(function() {
            $("#btn1").click(function() {
                var add = 0;
                $(".test").each(function() {
                    add += Number($(this).val());
                });
                $("#para").text("Sum of all textboxes is : $" + add);
            });
        }); 

Select allOpen in new window

any suggestions?