you need to make a transaction either in cask or bank journal. It's a kind of payement : Internal transfert

In the accounting dashboard, select the "More ..." button in the Cash box.

Here you can see in the middle the "internal transfer" option which open a the good menu , click create and here you can select where the money goes and how much you send money. You don't have to do the operation in the bank, it's automatic.

You can use this to, for example, create a "safe-deposit box" journal to have you daily cashbox and a secure one and have the tracability of transactions and inventory.

What you have to do :

For each cash, create an account and a journal which default debit and credit account is the new one (you can create the journal and the account in the same time)

If you use pos, it could be nice to select the good cash box in each pos in the "Available Payment Methods" section.

After that each cash box appears in the dashboard as each cash journal represents a cash box with its account and its amount.

In the same time, you can save money physically in the safe-deposit box, movement which is represented by the internal transaction described in my first post.

You can trace journal movements.