This article is from the Macintosh for sale FAQ, by Elliotte Rusty Harold firstname.lastname@example.org with numerous contributions by others.
In some sections of the U.S. a significant savings can
be realized by crossing a city or state line in search of a more
favorable sales tax rate. For instance in New York City sales
tax is 8.25% while right across the George Washington Bridge in
New Jersey it's 3.5% and a bit northerly in Westchester County it
drops to 6.25%. Drive all the way down to Delaware and there's
no sales tax at all. A New York City resident is supposed to
pay New York City tax even on purchases made out of state; but it
is perfectly legal to use the possibility of your going outside
the city to buy your computer to convince a salesperson to lower
their price. And in most other venues except New York and California
a purchase made by mail from a company outside the state of the
purchaser is non-taxable.