Setting the tax per carrier and region can be done, but multiple carriers will need to be created in order to cover multiple regions since tax rates would be different.  The following tutorial shows how to set the tax rate (based on states and territories of the United States) for a specific carrier in Prestashop 1.5.

How to set the tax rate for a specific carrier in Prestashop 1.5

1. Login to the Administration Panel as an Administrator
2. To set the option to apply both regular shipping and product-specific costs, hover over the menu bar where it says SHIPPING, and then click on CARRIERS in the drop down menu. This will bring you to a list of the existing carriers
3. To add a new shipper click on the green ADD NEW button, or select the shipping company that you wish modify and select the EDIT icon on the far right side of the screen. Then go to the CARRIERS section and scroll to Tax as per the screenshot below:
   
   
   
   
   
4. Click on the drop-down menu and select the specific tax rate that you wish to apply to the carrier
5. Select the green SAVE button in the top right-hand corner to save your selection

The taxes for each state and territory in the United States can be set through the menus in Prestashop. Be sure to make the appropriate tax rate available for all customers within a specific location to prevent incorrect taxation.