To compute sales tax in the US, you need a full address and product type(s). Not even zip code is granular enough to determine the tax rate. It can vary by coun

To compute sales tax in the US, you need a full address and product type(s). Not even zip code is granular enough to determine the tax rate. It can vary by county, township, inside/outside city limits, and in all these different combinations (literally thousands for the whole country) what items are subject to sales tax varies region by region too. For example, most states don't tax web design service, but there are a few that do. Most states don't tax advertising services, but a few do, and it depends what type of advertising is being bought. Passing on an address and a total to an API will do the trick 99% of the time, but technically, some of the businesses using that API are going to fail to collect sales tax in some cases where they should. I am hopeful that if enough state legislatures get serious about taxing internet sales, they'll band together to do some nationwide standardization. That kind of thing can't come down from the federal government; congress has no authority to tell a local municipality it can't levy its own sales tax, but state governments can. Kind of like how they all agreed (is it all? I think one or two didn't) to the Uniform Commercial Code so that the basic laws of sale contracts are the same in every state.