This is effectively a Roman banking question but specifically with respect to the custody and record keeping of slaves wages.
Dictionary of Greek and Roman Antiquities indicates a need for a lot of record keeping activity.
Slaves commonly had a peculium (money set aside for them) and there were debts back and forth between slaves, underslaves, slave owners.
Who was responsible for keeping the peculium records, the actual funds?
Were the debt records held in common with the peculium records or elsewhere, or were they informal?
Was there a public ledger or were the records only accessible to the slaver?
*- Dictionary of Greek and Roman Antiquities, John Murray, London, 1875.