There are different options for displaying tax rates on receipts. Configure the setting you'd like by navigating to Other Setup in Toast's back-end and selecting UI Options.
Scroll to the Tax Options section and select the appropriate configuration
The first option, Display each tax rate as a separate line itemizes each rate on the receipt.
The second option, Display all tax rates on one line consolidates the tax into a single line on the receipt. An additional field is shown to customize the label for this line. In the example below it is simply "Tax."
Be sure to save and publish your changes.