Cashiers don’t care, it saves them from whatever cringeworthy ’attention getter’ corporate policy like clapping or ringing a bell they’re compelled to do if you donate
I bought a bottle of water at the airport for $4.50
The POS kiosk asked me if I wanted to leave a tip. It was completely unintentional, but I chuckled at this dystopian scenario playing out, tapped "no" while starting to make eye contact with the cashier, they had a friendly smile so I just apologized but made sure to speak loudly and clearly over the airport sounds.
From her perspective, I must have looked like I boldly stared her in the eyes and chuckled at shorting her, then threw out an IRL #SorryNotSorry.
I hope her day improved after that unfortunate interaction...