Of all the sales tax packages, I have allways preffered CCH. Its not perfect, but I would say the best available. The tie in with Navision is not perfect, since its normally based on 5 igit zip code, but that is pretty accurate anyway, there are only a fe towns that break tax down futher than that, and they can be handled manually. The other problem is with Navision Returns if you use a ship to location, these are not done too well, so test that well.
By the way Paul, believe me Sales Tax really is much more complex than VAT. In the UK, you might get one change to the VAT rate for heating oil for pensioners once in ten years. Sales Tax changes by State, by County, by town by city every month. And not just the rates, but even the basic methods of calculation, sometimes is additive tax some time cumulative. And who remembers when Rockland county decided to increase sales tax by 0.005%. Sounds simple, except that Navision only allowed (back then) 2 decimals for sales tax rounding.