The option to automatically enable sales tax is unavailable in QuickBooks Online (QBO), ramesent. We can only manually select the boxes to enable it.
I understand that this feature is important to you. The automatic application of sales tax can assist you in managing how sales taxes are assessed without the need to repeatedly check the boxes.
Although this feature is currently unavailable, you can submit a feature request to our Product Engineers to address this issue as soon as possible. To send a feature request, please follow the steps below.
- Go to the Gear icon and select Feedback.
- Enter your comments or product suggestions.
- Then select Next to submit feedback.

You can either mark each customer as taxable or not or set a default taxable rate for all customers. To learn more about this process, you can check this article: Default customer sales tax rate in QuickBooks Online.
We value your input and suggestions. Your feedback will help us shape the future of QuickBooks products. If you have questions regarding sales taxes, please tag me by leaving a comment below, and We'll always lend a hand.