Victorian-era author and politician Benjamin Disraeli once said, "change is inevitable. Change is constant." He was probably complaining about all the jingling coins in his pocket. Yes, we hate having to carry a bunch of nickels and dimes, you never know when you need to make those small purchases.
Hence, the e-Coin. Think of it as a digital coin purse: it stores a digital representation of small dollar amounts. When you need to buy something, you select the price you want to settle hit send, and the e-cash is transmitted to a corresponding unit owned by the merchant.
If you think about it though, an easier solution would be to force all merchants, including sidewalk food stall vendors, to carry a credit/debit card machine. You get the same function, plus a card fits in your wallet better than a gigantic digital hockey puck.