horizontally center asp menu

I am unable to centre the menu bar horizontally. The no. of main menu items may inc./Dec. with each user login. This code makes the menu bar start at like 30% from the left.
Tried display:inline-block and display:table for #menuContainer.

If there are 5 main menu items and I set the width of #menuContainer to 30%, it appears centred.

ASPX:

    <div id="divMenu">
     <div id="menuContainer">
      <asp:Menu id ="menuBar" runat="server" Orientation="Horizontal" 
       IncludeStyleBlock="false">
        <item>
         <asp:MenuItem Text="Home"></asp:MenuItem>
         <asp:MenuItem Text="Folio">
           <asp:MenuItem Text="Nature"></asp:MenuItem>
           <asp:MenuItem Text="People">
             <asp:MenuItem Text="Tribe"></asp:MenuItem>
           </asp:MenuItem>    
         </asp:MenuItem>
         <asp:MenuItem Text="Contact"></asp:MenuItem>
        </items>
       </asp:Menu>
      </div>
     </div>

CSS:

    #divMenu
    {
    position:fixed;
    left:0;
    top:7%;
    z-index:2;
    width:100%;
    height:5%;
    }
    #menuContainer
    {
    width:50%;
    margin:0 auto;
    }
    #menuBar
    {
     position:fixed;
     top:5.3%;
    }
    #menuBar ul
    {
    list-style:none;
    background-color:silver;
    padding:0 5px;
    }