title: Nearest completed quarter
body: <p>Is there a C# function which will give me the last day of the most recently finished Quarter given a date?</p>
  
  <p>For example,</p>
  
  <pre><code>var lastDayOfLastQuarter = SomeFunction(jan 3, 2010);
  </code></pre>
  
  <p>would set lastDayOfLastQuarter = Dec 31, 2009</p>