Hello there, user113.
QuickBooks Online (QBO) is set to calculate tax rates by multiplying the amount and the rate per each line item while making sure it qualifies the standard set by your state. At this time, there isn't a way we can modify the calculation settings.
If you need to know more about managing GST in QBO, you can visit the articles shared by my colleagues above.
Feel free to drop me a reply below if there's anything I can help you with. Wishing you all the best!
