I can think of two. Using a pair of compasses set to 5cm; take a loop of non-elastic string 10 cm long (when looped, meaning the actual length of the string before looping is 31.4cm long) and pass the loop round a fixed thin peg or stick (the centre of the circle) and the other end of a loop around a thin pencil, then, keeping the loop taut, allow the pencil to trace a circle, just as you would with compasses.
The only other way I can think of is to find a circular object like a lid of a jar, for example, with a diameter of 10cm and simply draw round it, keeping the pencil as close to the edge of the object as possible.