This is a more common sloppy pronunciation that Americans tend to do, but generally other English speakers don't tend to. For example, I can't really think of any British accents that would say "hundred" in a way that sounds like "hunnid".

There are some combinations of sounds that occur in English that are genuinely difficult to pronounce carefully--they require a lot of quick tongue movement. They are often blurred in rapid, casual, or sloppy speech. These are all just examples of bad diction or mispronunciation: In "Hundred," the d-r transition is difficult, so it comes out as "hunnerd" or "hunn'd." "Library" is another--the b-r is difficult, and often the word is pronounced "Liberry." "February" is another; it is very common, but simply incorrect, to say "Febuary." It is so common that it is often misspelled "Febuary." (Here, there is a tendency to assume it should rhyme with "January.") "Nuclear" is famously difficult; former U.S. President George W. Bush and many, many, many other mispronounce as "Nucular." "Ophthalmogist" is difficult--all of the words with "phth" are difficult--and is frequently mispronounced and misspelled "Opthalmologist." "Naturally" becomes "Natcherly."

Its just sloppy English. No, Correctl, It is a hundred

But to be serious, "hunnid" is mostly used to refer specifically to 100 dollar bills. There is the term, "throwin hunnids". "keep it one hunnid" is a specific phrase used to mean, "keep it real": so, staying true to your convictions.

So one hunnid in this context is actually 100%, not 100.