I also confirm that sales taxes are a big mess, and all that expense to have Taxware's accountants sort it out for you is probably worth it if you have to charge taxes in every state.

We use Vertex where I work. Our current version is Oracle-based, but they support other platforms too. It is very expensive, but it works, decyphering all the state/country/city level tax rates. The send regular rate updates, and provide reports for auditing when the states call you on something.

Another complication not mentioned yet: at one time I had to alter our software to keep track of customers who lived in "unincorporated" areas of a county because they were complaining about being charged the city taxes.