The director is strongly hinting that very soon Basil will see "both sides of the coin" in regard to Dorian!

Also it brings home visually that, although different, "art" and "culture." are likewise linked inextricably:

"According to Wilde, art is a good thing; it's purpose is to be purposeless, and the only thing it should be is beautiful. Culture, on the other hand, is not necessarily a good thing – it can be a bad influence. Dorian Gray examines the weird gray area (pun very much intended) between the beauty of art and the fascinating corruption of culture."

www.shmoop.com/picture-dorian-gray/art-culture-theme.html

"He hides the painting in a storeroom and goes to look at occasionally. At one point Dorian is examining some large coins or medals and checking them against an illustrated coin catalog. The artist Hallward visits and lectures Dorian on his bad reputation. Dorian takes him to show him the painting and Basil is horrified. Dorian then murders Basil to silence him." Pictures 12, 13 and 14 of that page are relevant - plus 11 as Dorian brings out the box of coin trays.

The episode is covered in chapter XII, but I regard the coins as a device of the movie director, to show Dorian as blocking and distracting himself from Basil's lecture - maybe it is also the director's take on "Love of money is the root of all evil" (1 Timothy 6:10)

The sequence can be seen at (minutes:seconds) 62:50 to 65:20 of http://www.tudou.com/programs/view/c59m7ngY7-A