..Hi there, LLG27.
I'll help you with your tax.
Instead of adding a journal entry, you'll want to create a sales tax adjustment to show how much you owe. Here's an article to guide you through that: Create or delete a sales tax adjustment.
If you don't know how much amount to adjust, you can create a sales report for the period in concern to get the total taxable sales or do this per customer. You can even create a dummy invoice with one item, make sure the amount is equal to the total sale, and then assign a sales tax rate to it to get the tax amount. Do not save the invoice.
Here's an article for your additional reference: Sales tax in QuickBooks Online.
Let me know if you need more help with your tax. Take care and have a good one!
