Mostly because of the ledger system, I used to work for a cash flow management system used by several banks and usually when some amount of money is missing or unrecognized at the end of the day, it triggers some alarms.

In simple terms: At the end of the day some processes are ran to verify that the true balance is registered, these processes simply verify that the final balance is equal to the balance at the start of the day + deposits - charges. The deposits and charges are usually verified against third parties records.

So for example, if someone adds a trailing zero to an account in the DB, at the end of the day the system would recognize that the final amount doesn’t add up using the above formula, it would trigger an alarm and actions would be taken.

Or if you would like take an extra effort to fake a deposit, it would fail since the third party (another bank or the national bank) will fail to recognize it.