Could it be to incorporate a sales tax or VAT? As it is, you are going to pay the vendor the round sum, so the 1 cent which goes away could be attributed to VAT or some such.
--- ANOTHER THOUGHT ---
The 1 cent will not be recorded on the receipts. The 1 cent will also not be given back to you. Thats an unrecorded revenue
. Sheer profit in black.