Decimal currencies make things much easier for accounting reasons - so much simpler to total the columns. Earlier currencies might vary the coin values depending on the value of the different metals used.
Until 1971 Britain's coinage (in pennies) would have been 1,3,6,12,24,30,60,240 and 252 for the Guinea, which was no longer a minted coin by then, but was - and still is - used for certain transactions.