How can I apply sales tax to an entire estimate or invoice without individually checking each line item?

Let me provide you with clear guidance on how to apply tax to each line item on an invoice, @itskiki. 

When you add or create your products and services to QuickBooks Online, make sure to set them as taxable or nontaxable during the setup. This way, the tax rules you set will automatically apply each time you use these items. 

However, if a product or service should be taxable and isn’t set as such, you’ll need to manually edit the items and switch their tax status from nontaxable to taxable so when you create an invoice it will automatically apply on the Tax box.

Here's how:

1. Go to Sales and choose Products & Services. 
   
2. Click Edit next to the item you want to assign a tax category.
3. Select Edit sales tax. 
   
4. On the Other options section, choose whether the product is Taxable-based on location only or Nontaxable.
5. Hit Done, then Save and close. 
   
   
   

If you're a QuickBooks Desktop user, here's how to manually change the tax status: 

1. Hover over to the Lists menu, then select Item List. 
   
2. Double-click the item you want to edit. 
3. Under Tax Code, click on the dropdown arrow to choose whether to make that item Taxable or Non-Taxable. 
4. Click OK to save the changes. 

If you want to learn how to set up, edit, or deactivate sales tax rates, you can read and review this article for guidance and information: Set up your sales tax in QuickBooks Online.

If you need further assistance setting up taxes, don't hesitate to comment below. The Community is always here to help you. Have a great day!