The tax on an order will calculate based on the tax rate that has been set at the order and shipment level. 

Option 1: Apply a Tax Rate to an Order

• From the Order View page, click Actions > Edit.
• Under General locate Tax Type and update the selection.
• Click Save.
  
  

Note: This will update the tax rate for the current order but you may also want to 

update the customer with a default tax rate. For more information, see Customers - Financial.

Option 2: Apply a Tax Rate to a Shipment

• From the Order View page, hover over the name of a shipment and select the pencil icon.
• Shipping is Taxable should be toggled to Yes.
• Update the Tax Rate field.
• Click Save.

For more information, see Orders - Creating a Shipment.