Tin, abbreviated Sn on the periodic table, has multiple forms or allotropes. The one used commercially, white tin, is paramagnetic, meaning that it does not create a magnetic field of its own but is magnetized in the presence of external magnetic fields. Most "tin cans," though, are not made entirely of tin.
The tin can was patented by British inventor Peter Durand in 1810 as a novel method of food preservation. The earliest tin cans were made of iron coated with a thin layer of tin for corrosion resistance.
Tinplate steel, or steel with a very thin coating of tin, eventually replaced iron. In 1957, manufacturers began using aluminum instead. Aluminum simplified production by making cans from two pieces of metal rather than three. The bottom of the can is aluminum, while the cap is tinplate steel. In 1965, some manufacturers began coating steel cans with chromium instead of tin. Nearly all of these products are still colloquially referred to as "tin cans."
Iron, steel, tin and aluminum are paramagnetic materials -- so regardless of the composition of your "tin" can, it will be attracted to a magnet.