You can specify tax rates on a Delivery option at the price level if you have a Professional or Premium subscription. The field is available when editing or adding a new Checkout configuration. The field is a percentage value (no unit) and is not used within the Checkout. It will be returned along with the other delivery option details when fetching delivery options. See the API documentation. 

Add tax rate to an existing delivery option:

1. Log into nShift Portal and go to Checkout.
   
   
2. Edit the relevant configuration and go to Delivery options.
   
   
3. Click on the delivery option to which you want to add a tax percentage.
   
   
4. Expand the Tax rate section and fill in a value.
   
   
   
   
5. Click Save.

nShift Checkout will return the tax rate when options are fetched and you can process it as you wish to fit your business processes. The tax rate will be included below the price in the json. 

Example snippet:

Go to the API documentation.