A day-end closing is irreversible and can only be carried out once per calendar day.
The day-end closing literally ends the business day. It’s the final confirmation that any business transaction of the current day has been performed and that no changes shall be possible any more.
As soon as the day-end closing is carried out the end of day report is generated and all POS functions that create a business transactions (e.g. checkout, refund, cash withdrawal or cash deposit) are deactivated until the next calendar day breaks down.
If you’ve made a mistake while closing the day you won’t be able to make a corrective transaction up until the next calendar day. In order to comply with tax and accounting requirements the incorrect end of day report remains unaltered. Any (corrective) transaction is always part of the end of day report report it has been carried out.
In such cases it’s best to have a written explanation prepared before any tax audit. For example, you could add a note to your documents such as ‘Operating error while carrying out the day-end closing on 06/08/2018’. As a basic principle you should make sure, e.g. by appropriate job instructions, that these kind of mistakes are prevented, and that each day-end closing on any business day is carried out carefully.
Why we force daily closures and disallow reversing them
Legally, we could allow reversing the day closure, but technically this would not be trivial at all. For example, we had to make sure that a reversed end of day report would be marked and considered as invalid which is feasible regarding data in the system - but the printed copy of the end of day report will remain unchanged, which leaves the door wide open for accounting flaws or even fraud.
The general goal of the POS is to provide reliable data for accounting (= end of day report), which is exactly why we force the user to close each business day and disallow reversing it: The user confirms that all transactions of the day have been correctly checked out and that the amount of cash that actually is in the drawer equals the amount that should be in there (based on the user's POS transactions). If there has been any mistake (be it a wrong or a missing transaction) it will be found during the day closeout.
If we didn't force the user to do so daily, such mistakes wouldn't be found for days or at all and the user ends up with less reliable, flawed POS data.
Though we understand that not being able to reverse a flawed closure, we believe that this helps our users eventually: Our experience is that venues that do the closeout incorrectly once or twice, don't do so in the future. This is because they don't want to have flawed POS reports, so they have to be more accurate during checkouts and have to train employees better on how to close the day. If we allowed reserving the day closeout we would not encourage better and accurate usage of our software, we would rather allow making more mistakes.