Hello bdward,
Thanks for giving me an explanation of what you're trying to do with your RST and GST sales tax codes in QuickBooks Online. I know RST is a tax code that many business owners are using and that it makes things a bit tricky since it often only applies to a certain percentage of a charge, rather than the entire thing. I can point you in the right direction for this.
QuickBooks Online's sales tax module is fairly simple: set up a code and apply it to the appropriate line items or transactions. With what you need, it would be necessary to segment how the sales tax is applying, which isn't something the program is capable of doing at this time.
It sounds like you've got a good system going with manually adjusting the amount to override what the program is calculating, but I know it's easier to have a built-in feature to take some of the work out of entering transactions. For that, I recommend leaving the product development team your thoughts by following the steps in this article: How do I submit feedback? This helps us know the ways we can enhance the program to make managing your books run more smoothly.
I hope that helps! Give me a shout if you have more questions.
