I've got your back to help clarify the cash back option in the match screen, @tjohnson15.

I can see the relevance of this feature to you and your business. Currently, this is unavailable on the match screen. What we can do is to enter an adjustment to resolve the difference in a match.

Here's how:

1. On the Banking page, find an item with an amount that doesn’t match with a transaction you entered for it.
2. Choose the item, and once the row expands, click Find Match.
3. On the Match Transactions page, select the transaction to match. 
4. Once you select the transaction, scroll to the bottom of the table and click Resolve difference on the right.
5. Click Add new expense for money spent and then click Add new deposit for money received. 
6. Complete the fields in the table to add the adjustment.
7. Lastly, select Save.

I'm leaving you this recommended article. This will provide you with more information on how to manage your bank transactions in QuickBooks Online as well as on what are the options you can choose to allocate them: How to set and use banking rules for downloaded transactions.

Don't hesitate to comment down if you have other questions about your banking transactions in QuickBooks. I'll be happy to help you. Stay safe!