Taxes on the Purchase Order

Hi Seniors We have to make the Purchase Order having one line and unit price is 100 rupees but we also liable to give the 16 % tax on this Purchasing ..!!! so how do i paid that tax ??? normally to overcome this provision we just calculatle of 16% of unit price (i-e 100 in current example ) and the result (i-e 16) added to the unit price and hence it becomes 116... and we write in the po line unit price as 116 instead of 100 therefore now i am looking for the provision so that the tax of