I worked for Best Buy back in 2003. From what I remember it was 5% above cost, but I don't know if it was limited to in-store only.
What I do remember is that I had to get past a probationary period before I could use my discount, to deter people who tried to work there for a week to get a bunch of stuff cheaper.
Also, I remember I had to take a drug test, and the drug testing place was super strict-I'd never done one before and I felt super awkward getting told to keep my hands where they could see them and being forced to pee with the door open.