First, make sure all of your items have tax applied to them on your projects.
Then, ensure your taxes are correctly mapped to your tax types in QBO.
You can map the tax types from your account settings.
After selecting where you're mapping the taxes from the drop down, click the green 'Check Mark' on the far right side of your screen.
You'll need to map both the Country and the Province level to the desired Tax Rate.
Next, ensure you have a Zero-Rated tax type in your Policies and Taxes.
You'll need to add this to account for processing fees or any other item that you don't charge tax on.