Thanks for the details, user113.

The tax rates are multiplied by line item. Let me use the screenshot you attached as an example. Let's say 7% of $187.50 is 13.13, and on the other line item you have the same amount and rate and it's equal to 13.13. Hence, the GST @7% on $375.00 is 26.26. 

To help you look into the list of rates and manage them, you can check out your Sales tax centre. Just click the Taxes menu and click Edit GST. Then, Edit rates. You can click on a rate to see how they are applied to a sales or purchase transaction. 

My colleague attached articles that will help you handle sales taxes. You can use them as a reference. For further help, you can check out our Community Help articles. 

Always know that we're always available 24/7 so you can post and reply to use anytime. You take care and have a great day!