What amount turns a civil tax case into a criminal one?

I am often asked how big is the tax due to the IRS must be before it becomes a criminal matter.  Here is a new data point (from US Dep’t of Justice):

According to the indictment, Michael Ragsdale resided in Ashburn, Virginia, and owned and operated Foreign Service Auto (FSA), an auto repair business located in McLean, Virginia.  The indictment alleges that Ragsdale had decision-making authority over the business’s activities and controlled the business’s finances.  He was allegedly responsible for withholding employment taxes from FSA’s employees, paying the taxes over to the Internal Revenue Service (IRS), and filing its employment tax returns.  According to the indictment, from approximately the end of 2011 through 2014, Ragsdale did not file employment tax returns for FSA and did not pay approximately $112,000 in employment taxes.

If convicted, Ragsdale faces a statutory maximum sentence of five years in prison for each count of failing to collect, account for and pay over employment taxes.  He also faces a period of supervised release, restitution, and monetary penalties.

The full release is at: https://www.justice.gov/opa/pr/owner-virginia-auto-repair-shop-indicted-employment-tax-fraud