I’m $10 short

Okay so I worked from 1-10pm today so by the end i’m on auto pilot and not really paying attention. A customers change was $63. I gave the change and walked off, when I come back I saw the customer counting the change and I saw a $10 in his hand from the money I just gave him. Meaning I accidentally gave him $73 instead of $63. I’ve never done this before and want to know what are the consequences of being short as a cashier. I’ve been here 2 months.