Can invoice processing be set to automatic check the tax field or does this have to be filled in manually with each entry?

Yes, it can be, jessie. I'll elaborate on how it can be done so you don't have to manually fill out each tax section when creating invoices in QuickBooks Online (QBO).

In QBO, the options available to ensure taxes are automatically calculated and taken out of your sales transactions are to set up your customers and your product and service items as taxable. To set your customer as taxable, you can keep the Taxes box unchecked from its profile in the Additional Info section. Then, hit the Save button to apply changes, if there are any.

Aside from that, items added to the transaction should also be set as taxable. To know where this can be put up, you can follow the steps below:

1. Go to the Sales menu and select Product & Services tab.
2. Click the New button to create a new one or Edit to only make changes to an existing one.
3. Navigate to the Sales tax section and hit Edit sales tax.
4. In the Other options, select Taxable. Then, click Done.

After that, you can create your invoices and record their payments once your clients have settled them. 

Feel free to reply to this post if you have additional questions about managing sales transactions or require assistance with navigating the application. I'm just a few clicks away to help you. Stay safe!