The question was considered by the Swedish Supreme Court a few years ago, and it ruled that stores, transport services and such have no obligation to take cash

The question was considered by the Swedish Supreme Court a few years ago, and it ruled that stores, transport services and such have no obligation to take cash as long as they clearly advertise they're cashless. The legal reasoning is based on freedom of contract (avtalsfrihet). The shop has to take cash, but since what the shop does is enter a contract with you (agrees to sell certain goods for a certain price), it can choose to make cashless payment a condition of the contract. The same reasoning gives the shop the freedom to only accept paper bills and not coins for instance. This doesn't apply to public entities as freedom of contract is much more limited or non-applicable there - a public hospital must allow patients to pay in cash.