how to disable the tax calculation field in MIRO screen only for CreditMemo

Dear Expert

user want to create credit memo by MIRO transaction .But in table RBKP there no field to trace document ,that is invoice or credit memo document .i want to validate during credit memo, tax & with holding tax cannot calculate .I tried a lot badi but no badi or user exit is controlling at the time selection transaction & validating before save MIRO .

please help me.

Regards

Girish.