Inserting Pricing condition in Sales order when saving the sales order

Dear ABAPers,

My customers requirement is when saving the sales order new pricing condition has to be updated in the line item.for this i am using the User Exit 'USEREXIT_SAVE_DOCUMENT_PREPARE' ( MV45AFZZ).While saving the Sales order i am calculating the Price and updating in the Pricing conditions.

In XKOMV internal table i am appending the pricing condition.But the problem is ,it is not calculating the taxes and it is Updating in VBAK and VBAP.

How to do this.

Thanks & Regards,

Ashok.