Mothballs and Money

What do these two things have in common? Nothing usually. Yesterday I went to the bank to get some cash. When the teller handed me my money, she said that the money smells like mothballs as the money they received that day had that smell. So, do they store money in mothballs these days? All the bills were issued in 1999 or 2001 and were the older style bills. It is strange and smelly.