title: Round an NSString containing a decimal to two decimal digits
body: <p>Given the NSString "1.625", I want to round this to "1.63".
  How in the world do I do that?</p>
  
  <p>This is what i have now:</p>
  
  <pre><code>NSString *rateString = [NSString stringWithFormat:@"%.2f", [@"1.63" doubleValue]];
  NSNumberFormatter * f = [[NSNumberFormatter alloc] init];
  [f setNumberStyle:NSNumberFormatterDecimalStyle];
  item.rate = [f numberFromString:rateString];;
  </code></pre>
  
  <p>However, doubleValue converts 1.625 to 1.6249999999
  So when I round it to two decimal digits with @"%.2f", I end up with 1.62!</p>