The best way to turn off caching during development is to set these values in your user.config file (then touch web.config so the changes are picked up). Be sure to change them all back to "true" when running in production.
<add key="CombineCSS" value="false" />
<add key="MinifyCSS" value="false" />
<add key="CacheCssOnServer" value="false"/>
<add key="CacheCssInBrowser" value="false"/>
Jamie