Hi @StudioMH,

Thank you for your prompt reply. I'll answer your query about sales tax calculation in QuickBooks Online (QBO) for you. 

QBO automatically calculates the total tax rate for your transactions. It's based on these three things:

• Your customer's tax-exempt status
• Where you sell and where you ship
• What you sell

See this article for more details on this topic: Learn how QuickBooks Online calculates sales tax. It includes a sample calculation of sales tax along with screenshots for reference.

I'll also suggest this article for you: Add sales tax categories to your products and services. It has the steps on how to assign tax categories to your products and services, which allows you to track sales tax more accurately. 

Feel free to leave a comment below if you have other questions about the sales tax calculation in QBO. I'll get back to you as soon as I can.