The cashboxes used by the cashier are managed in Accounting > Chart of Accounts > Bank and Cash Accounts. The Cashbox is a specific type of account used by the Cashier Store. If you have multiple cashboxes, create the accounts here by clicking the blue +Account button, selecting Asset-Cashbox, and entering the name.  

If you want to add money to the Cashbox, click +New Transaction, and with the dropdown menu under Transaction Type, select Journal Entry (Transfer) to create a transfer from your bank account to the desired Cashbox. Then go to Store > Cashier to choose which Cashbox you would like to add the money to.  

After an event, you will want to create a Cash Tally Sheet by going to Accounting > Cash Tally Sheet. You can input event information, as well as how much money has come in. After submitting the Cash Tally Sheet, the Treasurer will be able to see cash in transit that has not been deposited yet. When you deposit the cash, go to Accounting > + New Transaction and select Deposit - Match from Pending from the dropdown menu under Transaction Type.  You will then select the desired Pending Cash Tally Sheet. Any surplus or deficit will automatically go to your Cash Tally Over/Under expense account.