You can leverage the power of HTML 5 features in your SharePoint Pages and custom pages.
By default, the master page "v4.master" page has been designed to work on XHTML guidelines for rendering the html controls and to be used work with IE 8.
So you need tweak this properties in your v4.master page.
In master page, leave the Register attributes as it is and add the above the html tag.
Secondly change to IE=9 in meta tag's' content attribute that all, save the file, do check in and publish the major version.