Who cares about Domain Rules?

namespace BusinessRules.Evolution_Three
{
    /// <summary>
    /// Australian Investor Business Rule Domain object specific to australian investors.
    /// </summary>
    internal class AustralianIncomeTaxEngine : IncomeTaxEngine
    {
        #region Methods

        /// <summary>
        /// Calculates the tax rate.
        /// </summary>
        /// <param name="income">The investor.</param>
        /// <returns>
        /// Returns a double representing the tax liability for the investor.
        /// </returns>
        public override double CalculateTaxRate(double income)
        {
            if (income >= 0.0 && income <= 6000.99)
                return 0.0;
            else if (income >= 6001.00 && income <= 25000.99)
                return 0.15;
            else if (income >= 25001.00 && income <= 75000.99)
                return 0.30;
            else if (income >= 75001.00 && income <= 150000.99)
                return 0.40;
            else
                return 0.45;
        }

        /// <summary>
        /// Calculates the tax liability.
        /// </summary>
        /// <param name="income">The investor.</param>
        /// <returns>
        /// Returns a double representing the tax rate for the investor.
        /// </returns>
        public override double CalculateTaxLiability(double income)
        {
            double taxLiability = 0.0;

            if (income >= 6001.00 && income <= 25000.99)
            {
                taxLiability += (income - 6000.99) * 0.15;
            }
            if (income > 25000.99)
            {
                taxLiability += (25000.99 - 6001.00) * 0.15;
            }
            if (income > 75000.99)
            {
                taxLiability += (75000.99 - 25001.00) * 0.30;
            }
            if (income >= 25001.00 && income <= 75000.99)
            {
                taxLiability += (income - 25001.00) * 0.30;
            }
            if (income > 150000.99)
            {
                taxLiability += (150000.99 - 75001.00) * 0.40;
            }
            if (income >= 75001.00 && income <= 150000.99)
            {
                taxLiability += (income - 75001.00) * 0.40;
            }
            if (income > 150000.99)
            {
                taxLiability += (income - 150000.99) * 0.45;
            }
            return taxLiability;
        }

        #endregion
    }
}