Not closing <li>s is much easier to maintain. Look at my web page for instance, https://ajf.me/

It's not only easier, but more readable to do this:

    <ul>
        <li>Item 1
        <li>Another item
        <li>Yet another item
    </ul>

Than this:

    <ul>
        <li>Item 1</li>
        <li>Another item</li>
        <li>Yet another item</li>
    </ul>