I'd be glad to help you further with your deductions, @alex-pearce.
Thank you for providing me with a screenshot.
There are several deductions which are pre-taxed in QuickBooks Online. Some of these deductions include:
This said, you can choose between these deductions as a payroll deduction for your employee.
Also, I recommend reaching out to your accountant about your deductions. This way, they can provide you with their insights on which pretax deductions to use.
You may refer to this article for more information: Supported Pay Types and Deductions Explained.
Feel free to leave a comment below if you have any other concerns.