In determining net proceeds of a cooperative, there shall be deducted from total proceeds:
(1) All operating expenses and costs;
(2) The cost of supplies, commodities, equipment, and other property or services procured or sold for patrons;
(3) The cost of services performed for patrons;
(4) All taxes and all other expenses;
(5) Reasonable and necessary reserves for depreciation, depletion and obsolescence of physical property, doubtful accounts, and other valuation reserves, all of which shall be established in accordance with usual and customary accounting practices.