If you are especially paranoid, there is a case for keeping records dating back beyond the statutory minimum period. In the event of a tax investigation throwing up an irregularity within "in-date" years they could allege that an adjustment is also appropriate for an earlier period. In that event the burden of proof would be on the taxpayer to counter such an assessment. While there would be no punitive consequence from having destroyed the records for that earlier period, it may make satisfying the burden of proof a particularly high bar to reach.
As I say, you would need to be paranoid (or knowingly cooking the books). They would not normally go back that far unless they reckoned on some level of fraud.