Paper Money Tainted with Cocaine

According to this article:

You’re not under arrest, despite the fact that you probably have some drugs in your pocket. Because there’s a good chance your paper money contains trace amounts of cocaine. According to a study presented August 16th at the American Chemical Society’s national meeting, up to 90 percent of American paper bills are contaminated with cocaine. In Washington, D.C., it’s as high as 95 percent.

So that's why money smells so good...