A new federal rewards program dishes out cash to people who turn in friends, relatives and employers for fudging their tax returns. For 24 years Vincent A. Spondello toiled away as an accountant for a group of related companies known as Monex, a large Newport Beach, Calif. precious metals dealer. A trusted employee, he prepared tax returns and was given such tasks as overseeing the destruction of old corporate documents. It turns out that some records that were supposedly destroyed he took home instead. In May Spondello sent 25 boxes of original Monex papers to the Internal Revenue Service--documents that...