Hello there, @SPARKLINGPOOL.
Currently, the option of adding taxes directly in your invoices isn't available in QuickBooks Self-Employed.
In the meantime, you can add a description of the rate and Tax amount. then you'll need to manually calculate the Invoice amount to include the Sales Tax.
For more reference, you can read this article:
Easy invoicing in QuickBooks Self-Employed.
Don't hesitate to click the Reply button if you have any other questions and concerns. I'm always here to lend a hand. Have a nice day