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

Good day, sdlumber.

You can mark the products and services as taxable. This way, you don't have to manually check the Tax box in your invoices or estimates. 

Here's how you can make the item as taxable:

1. Go to the Gear > List > Products and Services.
2. Click the Edit link of the item you want to modify.
3. Select Taxable from the Sales tax category drop-down menu.
4. Hit the Save and close button.

You can open this article to get more information: Sales tax in QuickBooks Online.

I'm just a post away if you have any additional questions about sales tax in QuickBooks Online. Thanks.