title: Force cpp_dec_float to round down
body: <p>I am using <code>.str(n, std::ios_base::scientific)</code> to print <code>ccp_dec_float</code>s.</p>
  
  <p>I've noticed that it rounds up.</p>
  
  <p>I am using <code>cpp_dec_float</code> for accounting, so I need to round downward.  How can this be done?</p>