power store wont handle that but eCart can.
you would need to create a tax rule in the eCart object for each zip code.
the zip code is stored in a session ariable named:
eCartCheckoutForm_shipping_postcode
in the tax rules, you can use the trigger "Based on session variable value"
if the session "eCartCheckoutForm_shipping_postcode" is equal to "Zip code 1"
using this method, you create a rule for each zip code using the tax rate for that zip
if the same tax rate applies to 2 or more zip codes, add those zip codes in the triggers section:
if the session "eCartCheckoutForm_shipping_postcode" is equal to "Zip code 1"
OR
if the session "eCartCheckoutForm_shipping_postcode" is equal to "Zip code 2"
OR
if the session "eCartCheckoutForm_shipping_postcode" is equal to "Zip code 3"
etc....
