How can I automate the tax management calculation in a purchase order?

Oracle Products: PO on EBS R12

Version: 12.1.3

Details:

When I create a purchase order I enter lines with the net value and the quantity of items I need. Later, after entering all the data I that each of lines have the tax associated with the purchase order calculated automatically. Right now, in the company that I am working, they have the solution for this using the Manage Tax option and entering the specific tax on the field Tax Classification of the form Additional Tax Information.

Now, all this process is manual, so I need to know if there is a way to set it up in order to work automatically.