Trek Global - 2005-08-24

When does the tax rate by Zip Code functionality apply?  We are trying to implement in California where each district has a separate set of taxes.  To test, I have set up two tax rates.  Both apply to US and California in the from and to fields.  Each has a zip code record maintained.  When I create an order to a business partner within one of the zip codes, shouldn't it choose that tax?  It does not, but seems to choose the first one it finds.

Any suggestions, or is this implemented all wrong?

Thanks, Joel