The plural of “Euro” is “Euro”. A Euro has 100 “Cent”. Think of it in terms of using “Moose” for your currency, but with smaller pockets. One Moose, Two Moose. One Cent, Two Cent. One Euro, Two Euro. The reason for not adding an “s” for plurality is simply this: not all languages add an “s” to make something plural.
I didn’t say that it makes any SENSE, but that’s the way it is.