private void addTipOrTaxToSale(CoreSale coreSale)
        {
            CoreTip tip = new CoreTip();

            tip.tipType = TipType.FIXED_AMOUNT;
            tip.amount  = Math.Round(18m, 2, MidpointRounding.ToEven);
        }
        public void OnRequestUpdateResponse(CoreResponse response)
        {
            CoreTip tip = new CoreTip();

            tip.tipType = TipType.FIXED_AMOUNT;
            tip.amount  = Math.Round(18m, 2, MidpointRounding.ToEven);
            CoreUpdate update = new CoreUpdate("UNIQUE REF");

            update.tipAdjustment = tip;
            Terminal.Instance.UpdateTransaction(update);
        }