How to unchecked all checked checkbox upon loading of dialog box contain JQgrid?

Hello as title above I have a problem that when I checked my checkedbox name ( $("#divLeaveIsHalfDay").click(function () ) that call the dialog box to open and contains my JQgrid name LeaveHalfDay.

function LeaveHalfDay() {
    var url1 = URL;
    $("#LeaveHalfDayDataEntryList").jqGrid({
        url: url1,
        datatype: 'json',
        mtype: 'POST',
        colNames: ['RowId', 'With Halfday <br /> Morning', 'With Halfday <br /> Afternoon', 'Date', 'Day'],
        colModel: [
                { name: 'rowId', index: 'rowId', hidden: true, editable: true, sortable: false, width: 80, align: 'left' },
                {name: 'cbox_leave_half', index: 'cbox_leave_half', editable: true, formatter: cboxFormatterLeaveHalfDay, formatoptions: { disabled: false }, edittype: 'checkbox', editoptions: { value: "True:False" }, sortable: false, width: 70, align: 'center' },
                { name: 'cbox_leave_halfPM', index: 'cbox_leave_halfPM', editable: true, formatter: cboxFormatterLeaveHalfDayPM, formatoptions: { disabled: false }, edittype: 'checkbox', editoptions: { value: "True:False" }, sortable: false, width: 70, align: 'center' },
                { name: 'LStartDate', index: 'LStartDate', editable: false, sortable: false, width: 70, align: 'left' },
                { name: 'LDate', index: 'LDate', editable: false, sortable: false, width: 55, align: 'left' }
             ],
        pager: $('#LeaveHalfDayDataEntryPager'),
        rowNum: 5,
        rowList: [5, 10, 20],
        sortname: '',
        sortorder: '',
        viewrecords: true,
        imgpath: '/Content/themes/redmond/images/',
        height: '100%',

        loadComplete: function (result, rowid) {
            var ids = jQuery("#LeaveHalfDayDataEntryList").getDataIDs();
            var len = ids.length, newLine;
            if (len < 5) {
                AddNewRowToGrid(len, "#LeaveHalfDayDataEntryList");
            }
        }
    });
    return false;
}

I want to unchecked all checked, checked boxes upon showing of my dialog box. This are my checked boxes cbox_leave_half and cbox_leave_halfPM in my grid. Thanks.