title: BigQuery - rounded outputs sometimes not really round
body: <p>I'm running <code>round</code> command on BigQuery but the output is not always as round as expected. 
  In addition it's not always the same values that are 'unrounded'.</p>
  
  <p>For Example, the Public dataset query:</p>
  
  <pre><code>SELECT year,month,day, sum(round(weight_pounds,2))as total_pounds, count(*) as cnt
  FROM [bigquery-public-data:samples.natality] 
  group by 1,2,3
  order by 1,2,3
  </code></pre>
  
  <p>Returns this output:</p>
  
  <p><a href="https://i.stack.imgur.com/poA1v.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/poA1v.png" alt="enter image description here"></a></p>
  
  <p>Is there a reason why the yellow marked values are not "fully rounded"?
  (If I rerun the query, other values might appear with .XX000001 or .XX99999 but the marked ones will be as expected rounded to the second decimal.</p>
  
  <p>Thanks</p>