Excise duty calculation process

Hi Experts,

I am doing a new implementation in one of my client and I am a beginner. I require your help relalted to the configuration of this excise duty.

The scenario is that I have to calculate Excise on basic invoice amount and CST on the cumulative amount of invoice + Excise @ 2%

Invoice amount:            Rs 1000

Excise duty@12.50%    Rs 125

Tota;l amount               Rs 1125

CST@2%                     Rs 22.5

Total amount                Rs 1147.5

Can you all help me so that I can map this in sap. Can someone please give me step by step process for the given scenario What should be be the steps I should follow for calculating excise and vat.

Can You also provide me with the tax procedure steps for mapping this calculation in sap.. It will be a great help

Thanks & Regards:

Jamshed