Is there a way to click just one button to add 10% tax to all my items or do I have to update each item individually and then mark the invoice as inclusive of tax?

Welcome to the Community, info-foodbyshykh!

At the moment assigning a 10% GST tax code to your items in one go is unavailable in QuickBooks Online. You'll have to edit your Products and Services, and assign a GST code on those items individually.

You can also set a default tax code in your sales form to be Inclusive, Exclusive or Out of Scope tax. Here's how:

1. Click on the Gear Icon.
2. Click on Account & Settings.
3. Click on Company tab.
4. Locate Default tax rate settings, and select Inclusive of tax.
5. Click on Save.

Then, when you record your sales or invoice your transaction will be set to the default tax selection set up.

You may want to check this article on how to Add inventory products in QuickBooks Online.

Feel free to contact us back here in the Community if you need more help with QuickBooks. Have a nice day!