Roman numerals are not base five, they are base ten.
I, II, III, IV, V, VI, VII, VIII, IX, X,
XI, XII, XIII, XIV, XV, XVI, XVII, XIX, XX.
I or any letter to the right adds one, I or any letter to the left, subtracts.
VI+ 5+1, 6
IV = 5-1, 4
L= 50
XL= 50-10 or 40
LX = 50+10, 60
M=1000
MM= 2000
C=100
D=500
1950= MCML
1998= MCMXCVIII
2013= MMXIII
It does not seem as though the idea of teaching Roman numerals via Superbowl games has worked.
You are right, Roman numerals are awkward and confusing.
The Romans managed to build the Parthenon nearly 2000 years ago, with a giant dome and it is still standing.
If you wondered how they did the engineering math with Roman numerals, the answer is, they didn't.
They used a sort of abacus resembling a cribbage board for the math.