Please try the yAxis' ticks' callback option:

    BarChart::create(array(
        ...
        "options" => array(
            array (
                'scales' => 
                array (
                  'yAxes' => 
                  array (
                    0 => 
                    array (
                      'ticks' => 
                      array (
                        'callback' => "function(label, index, labels) {
                            return ...; //format your number (label) here
                        }"
                      ),
                      'scaleLabel' => 
                      array (
                        'display' => true,
                        'labelString' => ...,
                      ),
                    ),
                  ),
                ),
              ) 
        )
    ));