How do I enable anonymous users to vote?
Looks like you need to enable the permission for anonymous users and also 

Drupal core poll module only allows one vote per anonymous IP address. check this link https://drupal.org/node/866168

The Poll Enhancements Module modifies this behavior to allow multiple anonymous votes from the same IP address. 


  This module enables anonymous users to vote on polls without page
  cache troubles or IP address restrictions. It is designed to work on
  top of core Poll module.