OK, this is a second hand story from perhaps 10 years ago.
Washington State - look up the auto sales tax regs
(WAC - Washington Administrative Code - i think)
Fellow bought a new car where no sales tax.
He then took a long vacation - he was retired - National Parks volunteer/jobs - visit relatives.
WHEN he brought this car into Washington - it was considered used - less sales tax.
I don't remember how many days to be considered used - might have only been 90.
Anyway, you get the general idea - you need to research your local laws/regulations on bringing used cars into your home state. And of course, WA State regs could have changed.
(Have family member buy in no sales tax state - then have them sell the car to you as used.
gee - you got a good price on that used car ....)
Of course, this is all second hand as I have NEVER done such a thing