the apple store charges tax based on where the item is shipped, so sometimes it may be better to buy in person, and sometimes it may be better to buy online.
sales tax at my home (memphis) is 9.25%, and that happens to be my billing address on my CC
sales tax at school (~minneapolis) is 6.5%, and that is my shipping address.
so if you were to, say, be buying something from apple for someone you were going to go visit, and they lived in a place with a lower sales tax than you, it would make sense to order it online and have it shipped to them instead of buying it in person and presenting it to them.
you just need to learn how to properly work the system. 😉
that make sense?