Best way to implement donation round-up on store commerce app

[zachbingham]

The client is looking to implement a process that prompts during check-out on the store commerce app and asks the customer if they would like to round up to the nearest dollar as a donation. Is there a recommended approach on how to best accomplish this? The initial plan was to add a pre-tender trigger that will automatically add a donation service item to the cart, the perform a price override on the donation item to set the price as needed. However, due to other business processes, they don't want to grant access to the price override operation to all cashiers. Any advice is greatly appreciated!