Sales tax in the US is exceedingly complex. It's simply out of scope for most companies to tackle without using a specialized sales tax vendor. To properly create a model of just US states' rules, you need to take into account dozens of factors like product type, exemptions, various address types, fulfillment info, and more.

You can get to a basic level of compliance fairly easily with state- and customer-based rates in select circumstances. But unless you dig deep, you will get things wrong, and you will only know about it when you get a potentially expensive audit years later.

Context: CTO of [Taxwire](https://taxwire.co), writing software for sales tax.