The two cousins, ages 2 and 3, went missing Oct. 12 while they were playing outside with friends.
The bodies of the girls were found Tuesday in community toilets in the town, which is located north of Johannesburg.
Four of the men have been charged with rape and murder.
The fifth man, who was arrested Friday after police offered a $10,200 reward for information, is expected to be charged on Monday with murder and kidnapping, the South African Broadcasting Corp. reported.
The 29-year-old's arrest sparked protests in the town, as residents demanded he be handed over to the crowd.
Police fired rubber bullets at the demonstrators who blocked a road and were throwing stones, the BBC reported.
The case of the four other defendants has been postponed while they seek legal aid.
The names of the five suspects are not being released.