In Sweden, even children now pay for their purchases with a debit card, these days. In fact, according to a press release from the Swedish Institute, digital payments via card or mobile app have become so widely accepted that many Swedes no longer carry cash at all.

A recent study from KTH-Royal Institute of Technology determined that Sweden can currently claim to be the world's leader in cashlessness.

"Our use of cash is small, and it's decreasing rapidly," said the study's author, Niclas Arvidsson. "Cash is still an important means of payment in many countries' markets, but that no longer applies here in Sweden."

According to the KTH study, there are now fewer than 80 billion kronor ($9.35 billion) in circulation; just six years ago total was closer to 106 billion.

Swedes today use plastic to pay for approximately 80 percent of all retail transactions, the Swedish Trade Federation has said. And retailers generally are not kicking about it so far, however small vendors might begin to push back.

"For small businesses and street vendors, the Swedish iZettle mobile payment solution for cards, or mobile app Swish, allow for easy payments," the release said. "As with traditional credit card transactions however, the new digital solutions are also starting to charge fees for businesses, frustrating some vendors who must cover such costs, even for small purchases."