Best Buy will fail simply for the following reason: http://www.bestbuy.com/site/Logitech+-+S715i+Speaker+for+Apple%26%23174%3B+iPod%26%23174%3B%2C+iPhone%26%23174%3B+and+Most+MP3+Players+-+Black/1114764.p?id=1218221913868&skuId=1114764&st=logite&cp=1&lp=7
vs
The sales tax advantage only applies if your products are the same price to begin with.
Look at any of Best Buy's PC component prices and you will see a huge difference between it and Amazon/other sites.