Why isnt my navigation rendering properly in IE9 - html

Question

Can anyone tell me why this nav renders as it should do in everything but IE9 and how i can work around this.
The project needs to be IE9 compatible.
This works fine in IE11
Here is my code. Thanks.
HTML
<li> Tills
<ul>
<li>Base Unit</li>
<li>Card Reader
<ul id="secondMenu" onclick="navClick()">
<li>Not Reading Cards</li>
<ul></li>
</ul></li></ul>
<li>Cash Drawer</li>
<li>Customer Display</li>
<li>Reciept Printer
<ul id="secondMenu" onclick="navClick()">
<li> Printing with blank areas </li>
<ul></li>
</ul></li></ul>
<li>Scanner
<li>Touchscreen
<ul id="secondMenu" onclick="navClick()">
<li>Black or faint pictiure</li>
<li>Distorted or fuzzy display</li>
</ul>
</li>
</ul>
</li>
<li> Self Check Out</li>
<li> Controller</li>
<li> Photo</li>
<li> iPads
<ul id="secondMenu" onclick="navClick()">
<li> Not connecting to BUK Corporate </li>
<ul></li>
</ul></li></ul>
<li> Handhelds</li>
<li> Personal Computing</li>
<li> Printing</li>
<li> Password Resets</li>
<li> Other</li>
</ul>
</nav>
Here is the CSS
nav {
display:block;
margin:8px 0px 10px 0px;
padding:0;
border-radius:10px;
text-align:center;
width:15.6%;
font-weight: 4000;
float:left;
z-index:999;
}
nav ul ul {
display: none;
}
nav ul li:hover > ul {
display: block;
}
nav ul{
list-style:none;
background:#5e6ea6;
}
nav ul li {
position:relative;
text-align:center;
border:4px solid #2f4389;
color:#FFF;
z-index:98;
font-size: 118%;
}
nav ul li a{
text-decoration:none;
color:white;
display:block;
background:#5e6ea6;
padding-bottom:7.9%;
padding-top:7.9%;
}
nav ul li:hover > a{
background-color:orange;
display: block;
}
nav ul ul{
position:absolute;
display:none;
}
nav ul ul {
background: #5f6975;
border-radius: 0px;
padding: 0;
position: absolute;
top: 100%;
font-weight: 4000;
font-size: 70%;
}
nav ul ul li {
float: none;
border-top: 1px solid #2f4389 ;
border-bottom: 1px solid #2f4389;
position: relative;
width:275px;
}
nav ul ul li a {
padding: 15px 40px;
color: #fff;
}
nav ul ul li:hover > a {
background: orange;
border:1px solid white;
}
nav ul li:hover ul{
width:100%;
position:absolute;
left:100%;
top:0;
}