C# Currency ("C") Format Specifier
To convert a number to a string we use the "C" (or currency) format specifier and it is representing a currency amount.

Let us see an example as follows.

double value = 175.87;

Now to display the above number until three decimal places, use (“C3”) currency format specifier.

value.ToString("C3", CultureInfo.CurrentCulture)

Let us see another example as follows,

using System;
using System.Globalization;
class Demo {
  static void Main() {
    double value = 275.66;
    // displays $
    Console.WriteLine(value.ToString("C", CultureInfo.CurrentCulture));
    Console.WriteLine(value.ToString("C3", CultureInfo.CurrentCulture));
 }
}

The output of the above code is as follows:
$275.66
$275.660