Like using a tricycle to commute to work, using ZIP codes to determine tax rates is a mistake. Originally intended to help mail delivery by identifying geographic areas and zones, ZIP codes lack the accuracy sales tax compliance requires. Overcharge customers by assigning a higher sales tax rate, they’ll get angry and complain or shop elsewhere. Undercharge customers and you’ll find yourself owing a hefty tax bill at some point down the line. ZIP codes lack the city-by-city, street-by- street, sometimes house-by-house variance in sales tax rates