Rebate

Hi All,

Buisness requires to calculate Rebate like for example -

100 bags - rebate is $1/per bag.

Now if customer buys 120 bags in certain period of time, he should get rebate on 20 bags x 1 usd = $ 20/- .

In Regular rebate customer gets rebate on 120 bags x 1/- per bag = $120/-

IS there way to configure this scenario in standard SAP that customer get $20/- rebate only not $120/ rebate?

Thanks,

Manish