我知道这不会给你解决问题的格式，但它是一个简单的解决方案来解决它。

I know this doesn't give you a format that fixes the problem, but it's a simple solution to work around it.

(5.00).ToString("0.00").Replace(".00","");  // returns 5
(5.90).ToString("0.00").Replace(".00", ""); // returns 5.90
(5.99).ToString("0.00").Replace(".00", ""); // returns 5.99