What's the use of the tax1, tax2 and tax3 columns

[joebordes]

You have to edit EACH product/service and add the taxes for that particular product/service for them to appear in the inventory lines.

In other words, pick a product or service, edit it, you will see the three active taxes appear in the price block, select the ones that apply to that product/service, even modify the values if necessary and save. Now go to an inventory module, select that product/service in individual tax mode and you will see the taxes you have selected for it.

Let me know how it goes.