Hello Abhimamyu,
I SRM tax is not calculated .. only you can determine Tax code based on condition which you can acchive by implementing badi BBP_DET_TAXCODE_BADI
you need to have fallowing option in SRM through config.
Customizing settings:
-> go to SPRO transaction -> IMG -> SRM -> SRM-SERVER -> Cross Appl-Basic Settings -> Tax Calculation -> Determine System for Tax Calculation
