title: Round numbers to the closest number with all digits equal to zero but the first digit
body: <p>I would round numbers to make all digits zero except one. So for instance, if I have <code>2341</code> I would round down to <code>2000</code> and up to <code>3000</code>, for <code>324</code> I would round down to <code>300</code> and up to <code>400</code>. Is there a way to round numbers so all digits are zero except the first one? 
  Ideally this should also work with small numbers, so <code>0.0568</code> would be rounded down to <code>0.05</code> and up to <code>0.06</code>. </p>
  
  <p>Function like <code>roundUp &lt;- function(x) 10^ceiling(log10(x))</code> would round up to the closest power of 10  [or lower power if changing <code>ceiling</code> for <code>floor</code>) but in this case <code>324</code> would be rounded up to <code>1000</code> whereas I would round it up to <code>400</code> and down to <code>300</code>.</p>