I found viewing the following video very helpful to understand both the complexity of the USA market, and the power of Xero's vision via partnerships with Apple and Avalara and others.
The USA has over 35,000 sales tax rules, 11,000 sales tax rates and 750,000 Buyer/Seller exemptions. If Xero can turn these complications into 'Beautiful Accounting Software' then the future may well be exciting.
Here's the link and thanks to RG367 for posting (Post # 6809)
https://www.youtube.com/watch?v=aSPf...ature=youtu.be
(Disc small holding and viewed as v speculative/risky. DYOR)