Suppose there are two submenus - this is the PHP code to add two submenus -
$reports=true;
JSubMenuHelper::addEntry(JText::_('COM_JGIVE_REPORTS'),'index.php?option=com_jgive&view=reports&layout=default',$reports);
JSubMenuHelper::addEntry(JText::_('COM_JGIVE_PAYOUT_REPORTS'),'index.php?option=com_jgive&view=reports&layout=payouts',$reports);
As you can see the 'view' for 2 submenus is same and 'layouts' are different

$document=JFactory::getDocument();
//override active menu class to remove active class from other submenu
$menuCssOverrideJs="$(document).ready(function()
{
$('ul>li> a[href$=\"index.php?option=com_jgive&view=reports&layout=payouts\"]:last').removeClass('active');
});";
$document->addScriptDeclaration($menuCssOverrideJs);
$document=JFactory::getDocument();
//override active menu class to remove active class from other submenu
$menuCssOverrideJs="$(document).ready(function(){
$('ul>li> a[href$=\"index.php?option=com_jgive&view=reports&layout=default\"]:last').removeClass('active');
});";
$document->addScriptDeclaration($menuCssOverrideJs);

It works well on Joomla 2.5.x. :)
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