Risk based, you should have an audit schedule/policies/procedures that your audit committee approves. It sounds like a lack of dual control, but I guess I am assuming the teller supervisor has conrol over ATM & individual teller drawers when necessary. If in doubt, discuss with your audit committee.
We are a very small bank as well, I am the internal auditor & compliance officer, Anytime I audit a cash area there is always someone else present. Vaults- officer, ATM- officer- teller drawers- that teller or their supervisor is present and watches the count. I think not having a second individual is just asking for problems, at least where cash is concerned.
And from my standpoint, I'm happy to have a second individual there- it protects anyone from pointing a finger at me if I find an issue/shortage.