This is a plain-English summary, not legal advice. If a specific obligation matters to your business, check it with your accountant or lawyer.
Seven years, for the tax records
Under section 22 of the Tax Administration Act 1994, businesses must keep sufficient records to determine their tax position, generally for seven years. In practice that covers invoices, quotes accepted, payment records and the working papers behind them.
It is why we treat financial and statutory records differently from everything else. Job photos and report media age out under your plan's retention window, with 30 days notice before anything is removed. Invoices, quotes, payment records, timesheets, incident entries and sign-offs are not on that clock. They stay for the life of your account.
Health and safety records
The Health and Safety at Work Act 2015 puts duties on a PCBU to manage risk and to keep the evidence of how it was managed. The practical version for a small crew is: the hazard was identified, the control was agreed, the person on site signed that they understood it, and the incident was recorded honestly at the time.
That last part is why our incident register has no delete button. Not a permission you can grant, not a confirm dialog: there is no code path that removes an incident. A record you can quietly tidy up later is not evidence.
GST, at 15%
Tax invoices need the right content and the right arithmetic. Software should compute the GST rather than trusting a typed figure, and the export to your accounting system should not need a human to correct it. If you are re-keying numbers into Xero, something upstream is broken.
The test worth applying
Pick a job from four months ago. Can you produce, in under a minute, who worked on it, what safety sign-off they gave, what parts went on, what you invoiced and when it was paid? If not, the gap is not a paperwork problem to catch up on later. It is the thing that bites when someone asks.