Hey Rochelley. Thanks for the reminder about the ability of check-marking the Subtotal option for print with the template customization. I'll pass on your feedback to our product development team for consideration. I know having the capability to see these things on your screen without having to print or use a PDF copy of the invoice is helpful.
I also wanted to share that BRC's steps of adding a second subtotal line after the previous one is working for me and giving me a subtotal of all the previous subtotals before taxes. Check out my screenshot below to see what I'm seeing. This not only appears on the screen, but would also appear on the printed version as well without using the subtotal checkbox in the template. It's not directly above the total with taxes portion of the invoice like it would be with the template option, but it's something that can be used as a workaround.
I hope that helps outline how to achieve this. I'm here if there are questions.