5 pounds on squat/dead and 2.5 on bench/press. Johnny (the man behind GSLP) is pretty adamant in the ebook about jumping by 2.5 only per session on the upper body lifts. You can get 1.25 plates at Amazon or other places. Gyms don't usually carry them.
Per session as in every time you work out? For example:
Monday: Bench 100
Wednesday: Press 102.5
Friday: Bench 105