We would suggest to allow only ONE vouchers for ONE transaction. Members have the choice to decide which vouchers amount to be use in their purchase on that transaction.
They may accumulate more points to entitle them to redeem for a higher value voucher if any and this will encourage members to re-visit your store(s) the next time for their unused point on redemption for vouchers. Usual customers will buy more than what's on their vouchers, hence, generate more sale.
Businesses with repeat customers result in a higher valuation.
*Business operates differently, please check with your Operations Team for clarification.