In Iran we have a lot of tombs and mausoleum that buried relative of Shiite religious leaders (Imam). Many people used to go there and request their desire or resolve a problem or pain, for this reason they pay cash and drop some money in tomb. They believe these dead saints are proxy of God.
An organization under charge of religious leaders every year collect all the money and they announced that last year altogether they gathered money a bit more than what we earn from selling oil in those places in entire of Iran.
You can see some pictures from mausoleum of saint Maesomeh (sister of imam Reza) in city of Qoom.