I'm going to ask the cashier to excuse the extra penny
Why do you need to do that? What is the plan for the extra penny?
I don't know, it depends on their reaction (for example they could be quite surprised or thinking why I ask)
She will probably need you to pay that penny or it will mess up her drawer balance. You should always make sure to square up your debt.
Eh, it's only a penny, I'll just throw it away and it's okay, I won't get in trouble for it.
A penny saved, is a penny earned! That cashier really needs that penny still, to have her transactions consistent. How do you think her boss would think if a cent or two were missing?