<p>How to, in C# round any value to 10 interval? For example, if I have 11, I want it to return 10, if I have 136, then I want it to return 140. </p>

<p>I can easily do it by hand</p>

<pre><code>return ((int)(number / 10)) * 10;
</code></pre>

<p>But I am looking for an builtin algorithm to do this job, something like Math.Round(). The reason why I won't want to do by hand is that I don't want to write same or similar piece of code all over my projects, even for something as simple as the above. </p>

Rounding a float to an integer is similar to (int)(x+0.5), as opposed to simply casting x - if you want a multiple of 10, you can easily adapt that.
If you just want to do integer math and are rounding it to ten, try (x+10/2)/10*10.
Edit:
I noticed that this response doesn't meet the original's author's request, and is also a biased form of rounding that I prefer not to do.  However, another accepted response already stated Math.round(), a much better solution.