The Problem with Third Farthings
The smallest value of coin in predecimalised British currency was the quarter farthing. I'm not sure how familiar my readership is with old British coins, but half a penny was called a halfpenny (known as a hayp-nee) and half of that was called a farthing. Thus a quarter farthing was worth about one sixteenth of a penny.
The next smallest coin was the third farthing which was worth one twelfth of a penny. While neither of these coins was particularly common, it does create an interesting anomaly for the currency. In a situation where you try to pay for something which costs a quarter farthing with a third farthing coin what change should you receive? In theory you should get a twelfth of a farthing back which would only be worth a ridiculous one forty-eighth of a penny. But we already know that that didn't exist; the quarter farthing was the smallest coin.
When designing a currency one of the requirements should be that there exists a coin of which every other coin is a multiple. Of the few currencies I have found that have broken this rule every one of them has had some previous smallest coin which they then took fractions of. This is a word of warning when trying to make smaller denominations, although quite frankly that would be heading in the wrong direction anyway.