I've read that when you buy a ticket to entry to the Taj Majal you get a "INR 500 for a one-time composite toll levied by Agra Development Authority for Taj Mahal, Agra Fort, Itimadi-ud-daula, Akbar’s Tomb, Sikandara and Fatehpur Sikri". How does it work? It means that if I pay 750 INR to get into the Taj Majal I don't have to pay to enter in the other places? And if that's true, I have to go the same day or the entrance is valid for the next day?
It's bureaucratic and complicated. (It's India!)
Each of the sites has a ticket, plus there's also a levy, and you need to pay both to get in. Each ticket is valid for one entry to that site only, and seems to be standardized at Rs 250 per site. The levy varies in value between Rs 10 and 500, but if you pay the maximum levy for the Taj Mahal, it's valid everywhere else as well for the same day only.