Here's a tutorial that shows one way to calculate totals for a set of columns in an HTML table:

http://beckelman.net/post/2008/11/13/Totals-and-Averages-of-Column-Data-on-Client-Side-Using-JavaScript-and-jQuery-Demo.aspx

This is the kind of thing that often shows up as a requirement in reporting tables and gives you a little jquery sample code for getting them in place.