Some history:
During the 17th century some private retailers issued their own small change due to the lack of official coins of small denominations. Around 128 businesses are known to have issued their own farthings, halfpennies and pennies in Wales. For England this figure rockets to over 15000!
These tokens were made from copper or brass, and it would seem the retailers involved were onto a good thing... The cost of production was very low. They could be given as change when a purchase was made and it seems it was all gain for the retailer. First, some of the customers would not return to redeem the value of their tokens. Second, due to their small size, many of the tokens were lost. Third, some retailers demanded more tokens than face value in exchange for goods, for example six farthing tokens for a penny worth of purchases. And finally some traders even refused to accept their own tokens!
Don.........
Source:
http://www.caerleon.net/archive/miscellany/farthings.htm