How to add supplier tax in Purchase Orders for Finished Good prices?

To add a tax to your finished good prices:

Step 1: Visit Setup > Inventory Setup > Finished Goods.
Step 2: Search for the finished good you want to add a tax to in the search field and click Edit against it.
Step 3: Key in the tax percentage in the "Tax for Purchase" field and click Update. The tax will be computed on Purchase Orders raised for the ingredient.