Is a 10% discount on the value of vouchers given to employees when purchasing with them from certain places considered a suspicion of usury, and what is the ruling on using these vouchers to purchase usurious items such as flour and salt?

Purchasing goods with checks is permissible, and the discount of a percentage of the price by some sellers does not affect this, as the matter is based on the mutual consent of both parties. Purchasing usurious items such as flour with checks is permissible and does not involve usury.