Is there a better way in C# to round a DateTime to the nearest 5 seconds?

Question

I want to round a DateTime to the nearest 5 seconds. This is the way I'm currently doing it but I was wondering if there was a better or more concise way?

DateTime now = DateTime.Now;
int second = 0;

// round to nearest 5 second mark
if (now.Second % 5 > 2.5)
{
    // round up
    second = now.Second + (5 - (now.Second % 5));
}
else
{
    // round down
    second = now.Second - (now.Second % 5);
}

DateTime rounded = new DateTime(now.Year, now.Month, now.Day, now.Hour, now.Minute, second);

Please note that I've found these two previous questions, however they truncate rather than round the time.

Answer 1

(Sorry for the resurrection; I recognize it's an old and answered question - just adding some extra code for Google's sake.)

I started with JayMcClellan's answer, but then I wanted it to be more generic, rounding to arbitrary intervals (not just 5 seconds). So I ended up leaving Jay's method for one that uses Math.Round on ticks and put it into an extension method that can take arbitrary intervals and also offers the option of changing the rounding logic (banker's rounding versus away-from-zero). I'm posting here in case this is helpful to someone else as well:

    public static TimeSpan Round(this TimeSpan time, TimeSpan roundingInterval, MidpointRounding roundingType) {
        return new TimeSpan(
            Convert.ToInt64(Math.Round(
                time.Ticks / (decimal)roundingInterval.Ticks,
                roundingType
            )) * roundingInterval.Ticks
        );
    }

    public static TimeSpan Round(this TimeSpan time, TimeSpan roundingInterval) {
        return Round(time, roundingInterval, MidpointRounding.ToEven);
    }

    public static DateTime Round(this DateTime datetime, TimeSpan roundingInterval) {
        return new DateTime((datetime - DateTime.MinValue).Round(roundingInterval).Ticks);
    }

It won't win any awards for bare efficiency, but I find it easy to read and intuitive to use. Example usage:

new DateTime(2010, 11, 4, 10, 28, 27).Round(TimeSpan.FromMinutes(1)); // rounds to 2010.11.04 10:28:00
new DateTime(2010, 11, 4, 13, 28, 27).Round(TimeSpan.FromDays(1)); // rounds to 2010.11.05 00:00
new TimeSpan(0, 2, 26).Round(TimeSpan.FromSeconds(5)); // rounds to 00:02:25
new TimeSpan(3, 34, 0).Round(TimeSpan.FromMinutes(37); // rounds to 03:42:00...for all your round-to-37-minute needs

Answer 2

The Ticks count of a DateTime represents 100-nanosecond intervals, so you can round to the nearest 5 seconds by rounding to the nearest 50000000-tick interval like this:

  DateTime now = DateTime.Now;
  DateTime rounded = new DateTime(((now.Ticks + 25000000) / 50000000) * 50000000);

That's more concise, but not necessarily better. It depends on whether you prefer brevity and speed over code clarity. Yours is arguably easier to understand.