Check-Box Order-of-Operation

        const double TaxRate = 0.0775;
        static double subtotal;
        static double tax;
        static double OrderTotal;

        private void radButtonHamburger_CheckedChanged(object sender, EventArgs e)
        {
            subtotal = 0.0;
            txtSubtotal.Clear();

            lblAddOnItems0.Text = "Lettuce, tomato, and onions";
            lblAddOnItems1.Text = "Ketchup, mustard, an mayo";
            lblAddOnItems2.Text = "French fries";
            grpBoxAddOnItems.Text = "Add-on items($.75/each)";

            /* add the extra items */
            if (chkBox0.Checked)
                subtotal += 0.75;
            if (chkBox1.Checked)
                subtotal += 0.75;
            if (chkBox2.Checked)
                subtotal += 0.75;

            subtotal += 6.95; // main course
            tax = (subtotal * TaxRate);
            OrderTotal = subtotal + tax;
        }

        private void radButtonPizza_CheckedChanged(object sender, EventArgs e)
        {
            subtotal = 0.0;
            txtSubtotal.Clear();

            lblAddOnItems0.Text = "Pepperoni";
            lblAddOnItems1.Text = "Sausage";
            lblAddOnItems2.Text = "Olives";
            grpBoxAddOnItems.Text = "Add-on items($.50/each)";

            /* add the extra items */
            if (chkBox0.Checked)
                subtotal += 0.50;
            if (chkBox1.Checked)
                subtotal += 0.50;
            if (chkBox2.Checked)
                subtotal += 0.50;

            subtotal += 5.95; // main course
            tax = (subtotal * TaxRate);
            OrderTotal = subtotal + tax;
        }

        private void radButtonSalad_CheckedChanged(object sender, EventArgs e)
        {
            subtotal = 0.0;
            txtSubtotal.Clear();

            lblAddOnItems0.Text = "Croutouns";
            lblAddOnItems1.Text = "Bacon bits";
            lblAddOnItems2.Text = "Bread sticks";
            grpBoxAddOnItems.Text = "Add-on items($.25/each)";

            /* add the extra items */
            if (chkBox0.Checked)
                subtotal += 0.25;
            if (chkBox1.Checked)
                subtotal += 0.25;
            if (chkBox2.Checked)
                subtotal += 0.25;

            subtotal += 4.95; // main course
            tax = (subtotal * TaxRate);
            OrderTotal = subtotal + tax;
        }

        private void btnPlaceOrder_Click(object sender, EventArgs e)
        {
            txtSubtotal.Text = subtotal.ToString("C2");
            txtTax.Text = tax.ToString("C2");
            txtOrderTotal.Text = OrderTotal.ToString("C2");
        }

        private void btnExit_Click(object sender, EventArgs e)
        {
            Application.Exit();
        }
    }
}