Hi TW and Saurav,
Apologies for going on a different tangent on this topic previously 
I believe that was a incorrect and bad advice.
Saurav: Coming to your requirement, I think I understand that you have both requirements together in rebate.
We could create a group of materials having the same rebate requirements I think called as Volume / Rebate Group - Material Master > Sales 2 View.
You can see the following SCN Thread for some help on this topic :
http://scn.sap.com/thread/1230954
Rest of the other things on where to enter the condition types and what criteria to be used for the value calculations are articulated by TW quite well.
Tell me if you have more questions.
Thanks.