To add a tax to your ingredient prices:

Step 1: Visit Setup > Inventory Setup > Ingredients & Sub Recipes.
Step 2: Search for the ingredient 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.

Alternatively, you can add tax when manually uploading your ingredients in a CSV file. To do so:

Step 1: Visit Setup > Inventory Setup > Ingredients & Sub Recipes.
Step 2: Click on Upload Ingredients.
Step 3: Click on Download all ingredients as CSV file.
Step 4: In the downloaded file, key in the tax percentage in the "tax_rate_po" column and save it on your computer.
Step 5: Next, visit Setup > Inventory Setup > Ingredients & Sub Recipes.
Step 6: Click Upload Ingredients and click Choose File.
Step 7: Choose the saved ingredient file from your computer and click Upload.