title: How to convert string to decimal with specific number of digits
body: <p>I have a small question regarding Math.Round function.
  I need the string "12.123456" to be rounded at 4 decimals. I used:</p>
  
  <pre><code> Math.Round(Convert.ToDouble(pData), 4).ToString()
  </code></pre>
  
  <p>where pData is defined as string, but the values are decimal with 7 decimals.
  My problem is that I expected to get every time the exact 4 decimals, but for some values it gives me only 2 (eg. 12.12 instead of 12.1200).
  How can I change in order to always get the needed 4 decimals?
  Regards,</p>