The director shall redeem any unused stamps that any wholesale dealer presents for redemption within six months after the purchase thereof, at the face value less 0.55% thereof if such stamps have been purchased from the director and are whole, complete stamps. The director shall prepare a voucher showing the net amount of such refund due, and the director of accounts and reports shall draw a warrant on the state treasurer for the same. Wholesale dealers shall be entitled to a refund of the tax paid on cigarettes which have become unfit for sale upon proof thereof less 0.55% of such tax.