Wrong tax calculation in MIRO

Dear Experts,

I am facing tax calculation problem while doing MIRO..

In PO the quantity is 40 Pcs. Net price is 12.50 GBP,

10% Discount on Gross.

Handling Charges 1500 INR.

When I have enter the Discount 10% the net price is changed to 11.25 GBP.

Tax code is TB(12.36%).

While doing MIRO the required Tax amount is 185.40 GBP, but it comes 179.22 GBP.

Please guide me how i can get the exact calculation.

thanks in advance.....

Regards,

Irfan