How to center a JqGrid

Question

<div class="center">
    <table id="results"></table>
</div>

<script type="text/javascript">
        $(document).ready(function () {
            $("#results").jqGrid({
                datatype: "local",
                height: 250,
                colNames: ['Inv No', 'Date', 'Client', 'Amount', 'Tax', 'Total', 'Notes'],
                colModel: [
                            { name: 'id', index: 'id', width: 60, sorttype: "int" },
                            { name: 'invdate', index: 'invdate', width: 90, sorttype: "date" },
                            { name: 'name', index: 'name', width: 100 },
                            { name: 'amount', index: 'amount', width: 80, align: "right", sorttype: "float" },
                            { name: 'tax', index: 'tax', width: 80, align: "right", sorttype: "float" },
                            { name: 'total', index: 'total', width: 80, align: "right", sorttype: "float" },
                            { name: 'note', index: 'note', width: 150, sortable: false }
                        ],
                multiselect: true,
                caption: "Manipulating Array Data"
            });
            var mydata = [
                            { id: "1", invdate: "2007-10-01", name: "test", note: "note", amount: "200.00", tax: "10.00", total: "210.00" },
                            { id: "2", invdate: "2007-10-02", name: "test2", note: "note2", amount: "300.00", tax: "20.00", total: "320.00" },
                            { id: "3", invdate: "2007-09-01", name: "test3", note: "note3", amount: "400.00", tax: "30.00", total: "430.00" },
                            { id: "4", invdate: "2007-10-04", name: "test", note: "note", amount: "200.00", tax: "10.00", total: "210.00" },
                            { id: "5", invdate: "2007-10-05", name: "test2", note: "note2", amount: "300.00", tax: "20.00", total: "320.00" },
                            { id: "6", invdate: "2007-09-06", name: "test3", note: "note3", amount: "400.00", tax: "30.00", total: "430.00" },
                            { id: "7", invdate: "2007-10-04", name: "test", note: "note", amount: "200.00", tax: "10.00", total: "210.00" },
                            { id: "8", invdate: "2007-10-03", name: "test2", note: "note2", amount: "300.00", tax: "20.00", total: "320.00" },
                            { id: "9", invdate: "2007-09-01", name: "test3", note: "note3", amount: "400.00", tax: "30.00", total: "430.00" }
                            ];
            for (var i = 0; i <= mydata.length; i++)
                $("#results").jqGrid('addRowData', i + 1, mydata[i]);
        });
    </script>

However the grid doesn't not appear centered where as everything else that uses that class is centered.

How can I center the grid? The CSS looks like this:

div.header
{
    text-align: center;
}