Hello ldorfman,
Welcome to the Community. QuickBooks is a powerful accounting program that offers a variety of tools and features that help you streamline your work. I'll be happy to share more information about setting up a default tax rate on your account so the taxes are uniform each time you enter a transaction.
In order to set up/change the default tax code on your account, you'll have to make the changes from the Account and Settings menu. To do this, click on the Gear icon > Account and Settings > navigate to the Advanced tab > look for the Accounting section > check/edit your Default tax rate and hit Save and Done.
Give this a try and let me know how you make out. I'll be here in case you have other questions. Otherwise, have a great rest of the week!