Hilton was arrested along with Rovero after Friday's Brazil-Netherlands match in Port Elizabeth on suspicion of possession of marijuana. Hilton's case was dropped at a midnight court hearing.
Rovero, a former Playboy playmate of the month, "acknowledged to be in possession of cannabis, and pleaded guilty," said a spokeswoman for South African police.
Rovero, a 31-year-old New Yorker, was sentenced to a fine of 1,000 rand ($130) or 30 days imprisonment, De Beer said.
Hilton wrote on Twitter later: "Hey guys, there's a lot of crazy rumors going around. Just want you all to know the truth. Everything is completely fine. I was not charged or arrested, cause I didn't do anything."
This isn't the heiress' first run-in with the law. In 2007, Hilton pleaded no contest to alcohol-related reckless driving and was sentenced to 45 days in jail.
AP contributed to this report.