The per-transaction fee is the whole problem
On a $4.50 coffee, a flat 10c per tap is 2.2%. On a $100 sale it is 0.1%. Same fee, twenty times the impact — which is why a rate that looks fine to a retailer is punishing for a café.
If your pricing has any fixed component per transaction, that is the first line to attack, ahead of the percentage.
Least cost routing is worth more here than anywhere
Most café payments are small debit taps, which is exactly the traffic least cost routing is designed to move to the cheaper network. It is frequently not switched on by default.
For a café doing a few hundred taps a day, that one setting can be worth more than the entire terminal rental.
Speed is a cost too
A few seconds per transaction is invisible on its own and decides the length of your morning queue. Integration between the point of sale and the terminal removes the keying step, and a terminal that has to reconnect between sales costs you more than its rental.
Worth testing at 8am rather than on a quiet afternoon.