A refiner, supplier, distributor, importer, exporter, terminal operator, and retailer shall maintain and retain records of all special fuel refined, purchased, imported, or otherwise acquired; of all special fuel exported, sold, distributed, and used; and of all inventory records, for a period of not less than three years. Inventory records include physical readings, metered readings of sales, delivery tickets, and delivery readings. The records are open to inspection by the commissioner or by any agent or employee authorized by the commissioner during business hours.