Welcome to Community! It's essential that your sales tax is set up accurately in keeping with government guidelines. Although there currently isn't a way to delete a sales tax code, QuickBooks Online provides the option to make them inactive, so they're no longer visible in your list. I'd be happy to assist!
Here's how to make a sales tax code inactive;
1. Open Taxes from the left menu and then select Sales tax (Take me there)
2. Click on Manage sales tax
3. On the Tax agencies tab, locate the tax agency associated with the sales tax rate you want to make inactive
4. Use the ▼ dropdown menu in the Action column next to the rate and select Make inactive
Note; You'll know the sales tax rate has been deactivated when you see Make active in the Actions column for that sales tax rate.