You may want to show a different icon with different viewport sizes. For example, compare the different sizes of the Google Calendar icon here:

http://setup.googleapps.com/Home/user-resources/google-icons...

You'll note the 16px icon uses square corners, while the other sizes have rounded corners.

There are other considerations as well, such as causing unintentional Moiré effects, and scaling DPIs in not-quite-powers-of-two (basically all of Android).