Can Tax Status be assigned to Inventory/Purchasing Categories?

Hi,

I would like to know if the following is possible?

I have setup a specific Purchasing Category Set and assigned it to a  Fiscal Product Classification.

I have then assigned the Category to an inventory item.

I have created a Tax Determining Rule and Condition Set and created a Tax Status Rule to default the Tax Status.

This work perfectly.

What happens if I don't have an inventory item? e.g I am in iProcurement. I buy a non-catalog item linked to the same category as the above. Can I get the Tax Status Rule to be based on the Inv/PO Category not linked to an Inventory item?