Hello LUNIC,

With the Automated Sales Tax, QuickBooks calculates the tax amounts based on the following: 

• Your customer’s tax exempt status
• Where you sell and where you ship
• Your service or product’s tax category

Since the calculations are now based on yours and client's addresses, we can no longer create our own sales tax rates when creating invoices. However, we still have an option to override it:

1. Open the invoice.
2. Click the See the math hyperlink below Sales tax.
3. You'll see the tax agency and standard rates applied to the invoice. You can click the pencil icon to do some changes.
4. Go to the Tax Categories and Totals section and click Override this amount.
5. Enter the Rate or the Amount and the Reason for changing it. Then, you can click Confirm.
6. Click Close.
7. Click Save and close.
8. Select Yes to confirm the action.

To get the correct calculation for your invoices, it'd be best to follow the Steps 1-7 of this article: Set up and use automated sales tax in QuickBooks Online.

If you have additional clarifications about it, please let us know. Additional information would be much appreciated.