It's very slightly annoying to me that people stopped properly abbreviating "mathematics" as "math's".
Very vague, weak citation: https://books.google.com/ngrams/graph?content=maths%2Cmath%2...
It was originally considered plural. That may even by why the transition from “mathematic” to “mathematics” happened in English.
But then I am from Australia.
The closest pattern to that is consistently not used with numbers of hundreds evenly divisible by ten. (OTOH, it is often used with “and”; the rule of not using and between components within the whole number portion but only to separate the whole number from a fractional part is not consistently applied in that informal alternative to the more formal thousands-hundreds form.)
ex: $270.50 -> Two hundred seventy dollars and fifty cents