Overview
Companies operating outside of the United States that require a Purchase Tax Code can add the available field to the Item Editor Page Layout.
Solution
Go to Admin > Page Layouts
Then find the row for the Item Editor and click the Edit icon on the right side

Now click the Purchasing tab and then find Purchase Tax Code in the list on the left and drag it into the page layout and click Save

Now open an Item and click Edit at the top. Then click the Purchasing tab and you will see and can set Purchase Tax Code for the Item.
