Somerville Gourmet Cakes & Pastries

Just been silently surcharged 5% on my visa card.
Purchased 2 pies, total $9.60 and found that my tap and go registered $10.10
He took my card and tapped behind counter. Not told about any surcharge, and surely he doesn't pay 5% fee. The law says that businesses now only allowed to charge up to their actual cost
Not happy as the pies were also very dried out. Purchased at 1pm