Just to add a little to Ravenhair's excellent answer...the earliest version of this saying was "All Lombard Street to an eggshell", which first appeared in print in 1763. The "China orange" version appeared in 1815 and another example was "All Lombard Street to ninepence". They all had to do with long-odds situations, as R said; the orange, however, was an actual fruit, as these were frequently imported from China in those days. Then, such an orange was seen as being typical of something of trifling value. Hence, "all the banks' money to a penny", as it were.