[Zope] dtml-in totals

I need to total variable from a dtml-in and give the result at the bottom. I can't seem to figure out what needs to be done to get this result. If I have the following: <dtml-in sql_statement> <table> <tr> <td> <dtml-var dollar_amount> </td> </tr> </table> </dtml-in> How do I total all the iterations of dollar_amount? Is there a way in dtml to put a variable in that stores a running total? TIA Rick