I have met a couple of Europeans who had registered their boats in other countries (I don't want to guess what flags
they were, but I think one was the Cook Islands
and one was somewhere in the Caribbean
. Take David's advice and do a goodle search). That way they did not have to pay VAT. You can then even sail in Europe
, as long as you are NOT a resident of the EU, as I understand it, and not pay VAT (following the 18 month rule).
There is no US sales tax, but each state is different so you need to check your state or the state you will buy the boat in.