Live Adding Numbers

1

I was wondering if it is possible to have a live “addition” of items. If I had radio buttons that you could select and add $5.00 it would add the cost to the top, and keep adding, or taking away etc. How would I do this? Also, I would not want the value of the radio field as $5.00 because in the checkout I am using PHP and will be calling the values. So is it possible to us onSelect, or something like this? HELP ME!