TAXINN and MM Pricing Schema Urgent

We want to configure for purchases made from Oil Companies. This should be calculated at the time of PO itself, so that correct PO can be given to vendor.

Background : The Oil sellers are basically dealers, hence the Assessable value for Excise and Selling price is not same.

So,

Basic Selling price = 1000, with Assessable value say 900 (to flow from MM pricing procedure)

Add : Excise duty  =      90 (@10% on assessable value 900) - from TAXINN

Sub tot                      1090

other charges             110 (manual entry from mm pricing)

sub tot                      1200

vat                               48 (4% of 1200)

invoice                      1248

Please tell how to do settings in MM pricing procedure, with condition types settings and TAXINN procedure.