Cristin, the link you supplied agrees with me.
• add 's to the singular form of the word (even if it ends in -s):
the owner's car
Also agreeing with me is The Royal Parks, the group that runs St. James's Park in London.
What flabbergasts me is that this is not something that is known by everyone whose name ends in S. I work with a guy named James (cleverly given the pseudonym of Tito on this blog) who doesn't know how to make the possessive form of his own name. Another reason that I hate him.
Our baby boy name (the one Rachel guessed on a totally lucky guess) ends in S and our son will have the rules of apostrophe use beaten into him. I don't want him going through life with people asking behind his back, "Did he huff paint fumes?"
Persephone made the valid point that the name Jesus only gets a free pass for Jesus Himself, not for Hispanics named Jesus. They have to write Jesus's.
Another misuse of the apostrophe that I forgot to mention earlier is the word "its." Even I am tempted (sometimes) to throw in an apostrophe, thinking, "It needs one because it's showing possession." Wrong! The word "its" is like the word "his," which shows possession without an apostrophe. It's a possessive pronoun. The only time you put an apostrophe with "it" is when you are leave out the second letter "I" of the phrase "it is."
Yet another trouble-making pair is "who's" and "whose." When the apostrophe is recognized as the tool it is, the choice is clear. When it's included out of duty, chaos ensues.