Interestingly the transition from pre-decimal (pounds and pennies) to decimal (dollars and cents) in Australia was a 2 year transition period from 1966, during which time both currencies were legal.

Combine this with the experiment of the last few years that provided Aboriginal welfare recipients with a card that could only be used for "essentials". You have everything in place in Australia for a switch to digital currency and consumption micro management. All tested for years in advance.