Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
it is e-mailed to you, or you can print the invoice off once your order is complete.

Welcome to the 21st century.
 
In store they give you a physical receipt.

Ive never encountered a situation where a printed out invoice that showed shipped wasn't accepted in lieu of a "physical receipt". It's pretty much the norm these days. Many stores beyond Apple offer not even getting the "physical receipt" in-store now.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.