Routine calculation in MIRO

Hi,

I am using routine for calculating tax in PO and the same routine gets called at MIRO also.Now the requirement is like that when the user enters the PO no. against which he is doing MIRO tax gets calculated from PO.Also user can change the value of condition type(for eg.ZASV) at the time of MIRO and then the tax should calculate on that.This is also working but if i have two line items for the PO in and user wants to change the condition value in both items its changing in only the last selected item because komv struture has the last item.I could not find anyother structure whcich keeps the changes values of both item.If anyone has any idea,kindly revert urgently.

Thanks & Regards

Madhu