I did that mostly because I couldn't get around using Numerals... makes my head spin. Imagine trying to do algebra or Calculus using numberals? No wonder the Romans never developed higher math like that.. and we only did AFTER we changed over to arabic after the Crusades and the Renaisaince.
Call it artistic liscence... or the Romans absorbed certain ideas from the Bedouins that may have helped them survive and industrialize and make PAPER currency. LOL. Try not to take it too seriously.
Bah, it's easy - LX over V equals XII! ...Hmm actually I see your point... lol. I've always thought it strange that no major civilisation progressed using anything but a base-10 system for numerics... I guess it's just easier to do on the fingers heh.