Either tatters or a19327 is telling the truth. Sorry, I couldn't resist. :)
Usually in these it pays to focus on the statement that is a different form than the others, so the last one. Suppose Michelle is telling the truth. Then Jimmy's statement is false. But we already assumed Michelle is telling the truth so the only way Jimmy's statement is false is for both Michelle and Toni to be truthful. But because Michelle was assumed to be telling the truth, Toni is not telling the truth. We have a contradiction, so our original assumption was faulty. Therefore, Michelle's statement is false. Now we know that at least one of Jimmy and Toni is telling the truth. It is easy to see that they are interchangeable, so both are truthful.