Sorry to burst bubbles here, but it's not how it work (I got my ps3 with this "deal")

 They take the value of the game, and if its less thant 10$ then round it to 10$. If its more, you will get the value corresponding. If its more than 20$, it will get cut back to 20$. Thats how it was explained to me. I got 130$ out of 10 game (7 x 10$ + 3 x 20$) and was quite disapointed at the add that in small characters asks you to see clerks for detail... oh well, everything was right in front of me and I did brought my 10 least played games so... I did the move.

So unless you're bringing back 10 copies of FFXII, don't expect the full price cut.