Depends how general you want to be.
My first choice would be: "On the Calculation with Hindu Numerals by Al-Khw?rizm?". I can't imagine the pain of trying to do financial management with Roman Numerals.
http://en.wikipedia.org/wiki/Arabic_numerals#Adoption_in_Europe
My second choice would be Luca Pacioli's textbook "Everything about Arithmetic, Geometry, and Proportions." which taught double-entry accounting to Europe (the Islamic cultures had been using it for hundreds of years before that)
http://acct.tamu.edu/smith/ethics/pacioli.htm
In theory it might be possible to use double-entry accounting with Roman numerals, but it would be very hard, which is why this is #2 and not #1. On the other hand, the Romans did have primitive accounting methods of their own:
http://en.wikipedia.org/wiki/Accountancy#Accounting_in_the_Roman_Empire
