Re: We're not in Kansas anymore, Tony.
"The timing is plausible, since decimalisation was in 1971, and banking mainframes did exist in the 60s, [...]"
A friend was manager for one of the high street banks. His twin children had been born on New Year's Eve - which was always the day when he couldn't leave the bank until they had balanced the books down to the last 1/2p (1/2d?). He always arrived home long after the party had finished.
He was finally at home for the twins' 21st birthday party in 1971. That was the year the computerised systems relieved him of the end of year chore.