Welcome to the Community. QuickBooks is powerful program that helps you get ahead with your work. I'll be happy to show you how to set up a default sales tax code in QuickBooks.
Here's how:
Go to Sales and select Customers.
Select the customer's name.
Select Edit.
Go to the Tax info tab in the Customer information screen.
Select a Default tax code from the dropdown menu.
Select Save.
I encourage you to try this out and let me know how you make out. I'll be a message in case you need anything else.