Format decimal to string in correct culture info

Why not decimalVar.ToString("F2", CultureInfo.CurrentCulture);. For format strings (the "F2" part) and what they do, see Standard Numeric Format Strings and Custom Numeric Format Strings

use:

Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US", false);

Add a format to the ToString: myDecimal.ToString("#.00") or myDecimal.ToString("C").

For a nullable decimal (decimal?) you will need to use the .Value property (myNullableDecimal.Value.ToString("C")) or cast the value to a plain (non-nullable) decimal. Be sure not to do this when the value is null or you will get an exception!

See the documentation for Standard or Custom numeric format strings.