It's kinda funny that you mention it. If we say to someone '99 hundred', they'd immediately understand it as 9,900. If we say 'hundred hundred', it's an immediate math problem trying to figure out how many zeros and what it's called. At least, that's how I'd react.
> If we say to someone '99 hundred', they'd immediately understand it as 9,900.
That's definitely untrue. In my native language we never mix tens and hundreds, and it always takes me a moment to parse that "thirteen hundred" means one thousand and three hundred.
Ah, I should have specified in the US. It's more common to say numbers between 100 and 10k as hundreds, unless it's exactly on a thousand. I think most people would say nineteen hundred, or 21 hundred for 1900 and 2100, but nobody would say 20 hundred for 2000(except for military time).