I have a WordPress site (on my localhost) that uses a <ul> for a custom menu. How can I change the CSS of a <li> on hover only if it has a <ul> sub-menu?

All the main menu items have a border-radius and I want to remove this on the current item (Services, below) for example:

    <div class="main-nav">
      <ul class="menu" id="menu-main-nav">
        <li><a href="#">Home</a></li>
        <li><a href="#">Services</a>
          <ul class="sub-menu">
            <li><a href="#">Item One</a></li>
            <li><a href="#>Item Two</a></li>
          </ul>
        </li>
        <li><a href="#>Contact</a></li>
      </ul>
    </div>

I can't find a CSS solution and I've tried jQuery too:

    $('ul.sub-menu').parent().hover(function(){
    $(this).addClass('no-radius');
});