I'm late to the conversation, but as many have said above, the plural of ringgit is ringgit. We don't use ringgits in conversation, except for fun, and when in Thailand, I have not heard at any time for the Thais to use bahts either. As an aside, to say "hundreds of ringgit" one could say "beratus-ratus ringgit", "ratus" being hundred as mentioned earlier.
Interestingly to note, our imported parking payment machines, with spoken instructions being in English and with fairly neutral U.S./U.K. accent, use ringgits. Which can cause occasional sighing and gnashing of teeth upon paying.
Like Gilead says, we do use "dollars" and "bucks" frequently in daily conversation. Also, we use "cents", despite also having the Malay alternative of sen (also plural), i.e. 20 cents/20 sen.
And having said that all, being a multiracial country, you could hear us speak of money in three or four different languages simultaneously, and this can also vary within the same language from state to state.
[I am Malaysian of Chinese descent, living in the capital, but English is my first language, with Malay and Cantonese in decreasing ability]