You might find it helpful to know you can also specify whole or partial zipcodes in the Advanced Tax Settings section of our Seller Admin > Cart Sales Tax/VAT Settings. For instance, if you entered these lines in that box:
857,6.6
85705,8.1
That would mean all zipcodes from 85700 thru 85799 would get charged 6.6% tax, except for 85705 which would get charged 8.1%.