TAXES ( high priority)

hi,

here i want configure the scenario that i want to purchase a excisable material from vendor, but he says the amount of material is say 1000 inr ( inclusive of taxes).

so when i m going for ME21N, I m not knowing the rates for material but system automatically calculates it from masters.

But at the time of GRN, i know the exact duty amount .so how i adjust the GRN excise duties with PO excise duties?