Numerical Extension Methods - C# .Net Core

NumericalExtensions.cs

using System;

namespace SimonGilbert.Blog
{
    public static class NumericalExtensions
    {
        public static double RoundByDecimalPlaces(this double number, int numberOfDecimalPlaces = 2)
        {
            return Math.Round(number, numberOfDecimalPlaces);
        }

        public static double RoundUpOrDown(this double number)
        {
            return PerformRoundedDivision(number);
        }

        private static double PerformRoundedDivision(double number)
        {
            double divisor = 1;
            double div = number / divisor;
            double floor = Math.Floor(div);
            double celing = Math.Ceiling(div);

            var difference = (div - floor);

            return difference < 0.5 ? floor : celing;
        }
    }
}