A little more difficult than that. I grew up in Pennsylvania. My zip code was for the town next to the township I lived in. There were taxes for stores in the town that weren't levied on the township (two different local gov'ts). Also, PA doesn't tax clothing while Maryland a few miles away does. So every item you sell would have to be categorized in some way (and maybe differently in different areas). So, every delivery address would have to be accurately mapped to multiple, overlapping taxing authorities (state, county, local, school district, etc.) and every item you sell would have to be mapped to multiple tax categories (clothes and shoes not taxed in A, clothes (but not shoes) taxed in B, shoes (but not work boots) taxed in C, etc.)