How to round to nearest hour using JavaScript Date Object

Round the minutes and then clear the minutes:

var date = new Date(2011,1,1,4,55); // 4:55
roundMinutes(date); // 5:00

function roundMinutes(date) {

    date.setHours(date.getHours() + Math.round(date.getMinutes()/60));
    date.setMinutes(0, 0, 0); // Resets also seconds and milliseconds

    return date;
}