I know it's fun to rag on Roman numerals, but they were never intended for totaling receipts. They were never designed for quick little sums, they were designed for engraving on massive long lasting objects like buildings and copyright notices on feature films, and they look pretty darned good there. Stop complaining that Roman numerals are not Arabic numerals. It's like saying counting on fingers is terrible because nobody has more than X them (That's 10 to you youngsters, or 0b1010 to you real smart alecks).

Judging a numeral by a standard it was never designed to meet is pointless. If you want to decide whether Roman numerals are a good number system or not, see if you can hammer them onto a building. I'd say you can. I may not like working with Roman numerals for grocery receipts, but that doesn't make them bad.