Record them at the point they arise, every day, and bank them intact rather than spending out of the till. Cash is where most enquiries start, because it is the only income with no automatic trail — a bank feed proves a card payment happened, but nothing outside your own records proves a £20 note did. So the discipline is a daily takings record, reconciled to what you bank, with any cash spending recorded separately rather than netted off. Under MTD the takings record must be digital, though you can record a day’s takings as a single daily total rather than every individual sale. What you cannot do is work backwards from your bankings at year end. That is not bookkeeping, and it does not survive contact with an inspector.