Visual Web Developer 2010

In some cases my TaxTxtBox displays a number that has no remainder. When my TotPriceTxtBox has a value with no remainder it still displays to the 100th place "34.00". Then in TextBox1 it truncates the zeros. I need the TaxTxtBox and Textbox1 to diplay zeros to the 100th place when the is no remainder. I.E. keeping it in a money format. I tried using Decimal instead of double but I get an error saying that you cannot apply the *,+ operand to a Decimal or Doudle. Here's my code:
Code:
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protected void EnterBtn_Click(object sender, ImageClickEventArgs e)
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       {
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           Decimal res = Decimal.Parse(PriceTxtBox.Text);
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           res = res * Decimal.Parse(QtyTxtBox.Text);
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           TotPriceTxtBox.Text = res.ToString();
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           if (TotPriceTxtBox != null)
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           {
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               Double rs = Double.Parse(TotPriceTxtBox.Text);
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               rs = (rs * (.070)) + Double.Parse(TotPriceTxtBox.Text);
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               Double ts = (rs * (.070));
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               Double tt = ts + Double.Parse(TotPriceTxtBox.Text);
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               Double output = Math.Round(rs, 2);
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               Double output2 = Math.Round(ts, 2);
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               Double output3 = Math.Round(tt, 2);
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               TextBox1.Text = output3.ToString();
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               TaxTxtBox.Text = output2.ToString();
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           }