Hello sales135,

Currently, assigning tax codes is done per item. Hence, the tax calculation is also based per item. You'll need to enter them one at a time.

Aside from that, you can add the tax codes to the item setup. This'll save you time when you use the items to create a transaction. Here's how to do it:

1. Click Sales on the left menu and go to the Products and Services tab.
2. Look for the item and click Edit.
3. Enter the tax code in the Tax or Purchase Tax field.
4. Click Save and close.

With this, you don't need to enter the tax codes manually in the transaction page.

You can also use these articles to know more on how sales tax works in QuickBooks Online: 

• How Cash and Accrual accounting affect sales tax.

• Manage a tax rate change

We're always right here if you need anything else.