Your coin pyat'ak probably measures about 38mm and one onliner values it at US$150 . Without being able read or translate Russian, each kopek denomination is distinquished by its diameter. This coin would appear as big as an IKE dollar. An excellent coin from within a hugh collection of finds.
Don.....
That pic is of the ten kopek, not the 5 kopek as found. Your referenced site does show, however, an example of each denomination, including the found '5'.