Nowadays, most corpses are embalmed before burial.  Back in Victorian times when Dickens was writing, this was not so -- as muscles would relax and then firm under rigor mortis, corpses would be "frozen" in the position in which they died.  Many times this meant the jaw was slack and the mouth and eyes were open. To avoid having to look at the dead's final facial expression, immediately after death, common practice was to shut the jaw and keep it closed by wrapping a bandage around the head.  Dickens' readers would have been familiar with the practice, but a much later English work additionally suggests how eyelids were kept closed: "Now my advice for those who die / declare the pennies on your eyes...."