I think that the reason our number system has 10 numbers before it goes into 2-digit numbers is because of our hands and feet. Most people have 10 fingers and 10 toes. So a few thousand years ago when humans were developing our number system they all looked at their hands and feet. They all had 10 fingers and 10 toes. So the roman numeral system was probably based on having 5 fingers on each hand, a total of 10 fingers, and 2 hands which is why their numbers had different symbols for things that started with 1,5,2 because of their hands and feet. But if people had 6 fingers on each hand then we would count like this:

Key/Legend

0=a  1=b  2=c  3=d  4=e  5=f  6=g  7=h  8=i  9=j  %=k ~=l

Note: For now % will be the number that comes after 9 if we had 6 fingers. Also, ~ will be the number after %.  

With 5 fingers we count:

0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20 etc.

With 6 fingers we would probably count:

0,1,2,3,4,5,6,7,8,9,%,~,10,11,12,13,14,15,16,17,18,19,1%,1~ etc.

I don’t know if you actually understood that but if you did then feel free to attempt to use it for some extra-credit project just give the author Crashnibbles credit, don’t copyright it, patent it, or anything else like that and please comment on if you understood or not and if you successfully got extra credit for “borrowing” it. I hope that you found this useful (if you understood it at all)