Hello @kristen_678 thanks for your post. While Square POS does not offer the ability to show a "donation" screen or button to your customers, you could create ITEMS in your inventory and call them $10 Donation, $20 donation, etc...you could even set these up in your POS checkout screen. When you are checking out a customer, you can ask them if they'd like to make a donation, suggest an amount, and then "add" that inventory item to their order.
You may want to check the sales tax requirements for this kind of donation in your state. Some donations may be sales-tax free, so when you create these donation items you'll want to make sure the sales tax is either turned ON or turned OFF for those items.
If you are using a barcode scanner, you could even setup a table tent with a printed barcode on it, and when a customer agrees to a donation, just scan the appropriate barcode on the table tent to add that donation to their sale.
