retrieving live data from $wpdb

I am trying to run some live data feeds into my page. I am using the global $wpdb variable to access the custom tables and data which works great.

However I have a timer running which re-runs the $wpdb->get_results() and rewrites the results into a div. But after the inital run through the data is not updated as if the $wpdb is not updated.

The function I have is:

<?php
	global $wpdb;
	$total = 0;
    	$sales = $wpdb->get_results( "SELECT NET_AMOUNT FROM wp_dailysales");
	foreach($sales as $sale)
	{
	    $total += $sale->NET_AMOUNT;
	}
	$total = $total;
?>

If I refresh the page it pulls in the correct data, just not on the timer. Is there a function that I am missing?

Thanks

Simon