Al Capone was convicted of failing to file a tax return.
According to Wikipedia:
Assistant Attorney General Mabel Walker Willebrandt recognized that mob figures publicly led lavish lifestyles yet never filed tax returns, and thus could be convicted of tax evasion without requiring hard evidence to get testimony about their other crimes.
These days, if you file late, you get penalized financially, not go to prison.
Would Al Capone's crime merit imprisonment today?