Calculation of Tax amount wrong in MIRO

Hi

I am facing issue in the tax calculation at the time of MIRO. In the screen shot i am using amount is 554 and 1% CST it should be 5.54 instead of 12.74. This problem is coming in all tax codes but not in all MIRO. As per my observation if i am using discount condition in PO then this problem is appearing otherwise in other POs this is not happening. Please suggest.

Regards

Ajay