In Supervalu anyway, one voucher is no problem but try to scan a second voucher assistance is called for, not sure if its the same with all their self service tills.
Once you've spent enough to cover the vouchers of course you should be able to cash in more than 1 voucher surely, any work arounds.
Once you've spent enough to cover the vouchers of course you should be able to cash in more than 1 voucher surely, any work arounds.