Thank you sooo much!!! That appears to be working perfectly! I made a few test users, one that lives in Denver and one outside of Denver. I set the Local Sales tax MOD to match on the City name, and it calculated the taxes properly for both customers.

I have been dreading trying to figure that out - you have made my day!!! This should become part of the ZenCart core, and an example like you just gave should be in the 'manual'!!

Thanks again,
Will