EBT at PO and Requisition

HI EXPER, we use to calculate the tax manually of each line which is 16 % and then add it to the unit and in PO we write the amount in the unit price coloum with tax but it is our cleint requirement that there must have a provision on the basis of which we can application can calculate the automatically ..... my friend told me about EBT ... so can u plz suggest the specific note and as well as help me while doing the setups too .......... we have three operating units .. so kindly suggest me the provision ..???
THANX IN ADVANCE