* There are over 23,000 distinct tax rates in the US. Most of these can be nicely pigeonholed as 'State', 'County', or 'Municipal'. Some can not.
* There are a handful of cities with multiple municipal tax rates. Most of these straddle counties. A small handful of them, perplexingly, don't.
* Most states charge tax based on the three(ish!) rates applicable at the sale's destination. Several charge based on the origin.
* Some states charge tax on shipping. Some states charge tax on shipping and handling. Some both, some neither.
* Three states only charge county and municipal level taxes if the destination is located in a county that the business has a phyiscal presence in. Of these three, one does something subtly different still.
* Figure the 5-digit zip code is sufficient to identify the applicable rates at a given address? Nope. You actually need to geolocate the street address to get it right sometimes.
* There are a nearly-unfathomable depth and breadth of exceptions on a type-of-goods basis (selling clothing in New York? It's exempt if it's under $110, but only from State tax, and additionally county tax if the destination is in one of 14 specific counties, unless it's in the cities of Norwich or Oneida, in which case the County tax applies again.)
This astounds me as a Software Developer and a Canadian (we have vastly simpler Sales Taxes). How they expect Joe Merchant to be able to charge all these taxes correctly without radical simplification (and unification) of tax codes is beyond me. Very far beyond me.
--EDIT--
After reading the full bill, it's not as bad as I previously thought (logistically, ignoring the more-taxes discussion). However, it is still pretty bad.
Salient points:
* One central authority per state means at most ~50 points of contact. This is better than 23,000, but not exactly good.
* Doesn't apply to merchants doing less than $1M/yr in business.
* States are required to provide a database of rates and boundaries. As worded in the bill, it's unclear whether this means zipcodes or bounding coordinates. Geolocation is not a cheap service at scale.
* Each state is required to provide software to calculate rates for a given sale. Given government, this will likely be a desktop Windows app that does not integrate cleanly with any server-side infrastructure, nevermind the fact that there will be 50 likely-distinct pieces of software.
On the other hand, with states actually being encouraged to publish their rates in a freely-available machine-friendly format for once, perhaps we'll see some startups pop up around this problem to ease the pain.