如果值为0，则很少需要空字符串。

decimal test = 5.00;
test.ToString("0.00");  //"5.00"
decimal? test2 = 5.05;
test2.ToString("0.00");  //"5.05"
decimal? test3 = 0;
test3.ToString("0.00");  //"0.00"

排名最高的答案是错误的，浪费了（大多数）人10分钟的时间。

最适用的解决方案是

decimalVar.ToString("#.##");

排名靠前的答案描述了一种格式化十进制值的字符串表示的方法，它是有效的。

但是，如果您确实想将保存的精度更改为实际值，则需要编写如下内容：

public static class PrecisionHelper
{
    public static decimal TwoDecimalPlaces(this decimal value)
    {
        // These first lines eliminate all digits past two places.
        var timesHundred = (int) (value * 100);
        var removeZeroes = timesHundred / 100m;

        // In this implementation, I don't want to alter the underlying
        // value.  As such, if it needs greater precision to stay unaltered,
        // I return it.
        if (removeZeroes != value)
            return value;

        // Addition and subtraction can reliably change precision.  
        // For two decimal values A and B, (A + B) will have at least as 
        // many digits past the decimal point as A or B.
        return removeZeroes + 0.01m - 0.01m;
    }
}

单元测试示例：

[Test]
public void PrecisionExampleUnitTest()
{
    decimal a = 500m;
    decimal b = 99.99m;
    decimal c = 123.4m;
    decimal d = 10101.1000000m;
    decimal e = 908.7650m

    Assert.That(a.TwoDecimalPlaces().ToString(CultureInfo.InvariantCulture),
        Is.EqualTo("500.00"));

    Assert.That(b.TwoDecimalPlaces().ToString(CultureInfo.InvariantCulture),
        Is.EqualTo("99.99"));

    Assert.That(c.TwoDecimalPlaces().ToString(CultureInfo.InvariantCulture),
        Is.EqualTo("123.40"));

    Assert.That(d.TwoDecimalPlaces().ToString(CultureInfo.InvariantCulture),
        Is.EqualTo("10101.10"));

    // In this particular implementation, values that can't be expressed in
    // two decimal places are unaltered, so this remains as-is.
    Assert.That(e.TwoDecimalPlaces().ToString(CultureInfo.InvariantCulture),
        Is.EqualTo("908.7650"));
}

所有这些都没有达到我所需要的效果，即强制2 d.p.并舍入为0.005-0.01

强制2 d.p.需要将精度提高2 d.p.，以确保至少有2 d.p。

然后四舍五入，以确保我们的d.p不超过2。

Math.Round(exactResult * 1.00m, 2, MidpointRounding.AwayFromZero)

6.665m.ToString() -> "6.67"

6.6m.ToString() -> "6.60"

decimalVar.ToString("#.##"); // returns ".5" when decimalVar == 0.5m

or

decimalVar.ToString("0.##"); // returns "0.5"  when decimalVar == 0.5m

or

decimalVar.ToString("0.00"); // returns "0.50"  when decimalVar == 0.5m

如果您只是需要显示，请使用string.Format

String.Format("{0:0.00}", 123.4567m);      // "123.46"

http://www.csharp-examples.net/string-format-double/

“m”是十进制后缀。关于十进制后缀：

http://msdn.microsoft.com/en-us/library/364x0z75.aspx