How to set the settings to be able to apply multiple sales taxes to our sales invoices (without changing the base amount)?

Thank you for posting in the Community, Justine. I can help you apply multiple sales taxes to your QuickBooks Online invoices.

To begin with, you can use the Group rate feature to combine multiple tax rates into a single rate. This will allow you to apply one combined rate to the invoice, although it won't show the individual tax components on the invoice itself.

Here's how:

1. Go to Taxes and then select Group rate.
2. Fill in the necessary details like Group name, Description, and Tax rate.
3. Please ensure that the Applicable on dropdown choose Tax amount.
4. Once done, click Save.

Next, when creating an invoice for each product or service, click the Add subtotal button under the list of items. This will insert a subtotal line that sums up the amounts above it.

Furthermore, you can check this article to learn how to apply a sales tax category to your products and services: Add a sales tax category to products and services in QuickBooks Online.

Please let me know by leaving comments below if you have further concerns about applying multiple sales taxes. I'll be here to lend a hand.