Adding Rounded doubles to label

I'll use the Math.Round function, but there happends something strange.
If i have a numer like 10.0012356 he adds with round(10.0012356) only 10, and not the wanted 10.00 
But if i have 10.534, he adds 10.53, so then its ok.
How can i change that?

I use this code right now:
 double PriceIn = PriceExcl * ((BTW + 100)/100);
            lblPriceEx.Text = "€" + Math.Round(PriceExcl, 2).ToString();
            lblPriceIn.Text = "(" + Math.Round(PriceIn, 2).ToString() + "incl.)";
...