I used this in 6.0.10 for a while, it may still work in later versions.
in classes/cubecart.class.php
change
$GLOBALS['smarty']->assign('LATEST_PRODUCTS', $products);
To:
$lp_rand_keys = array_rand($products, 6); // Make sure there are 3 or more 'featured' products
foreach ($lp_rand_keys as $rand_key) $lp_rand_products[$rand_key] = $products[$rand_key];
$products = $lp_rand_products;
$GLOBALS['smarty']->assign('LATEST_PRODUCTS', $products);
This will limit the amount of 'latest products' to 6 (so change if you require more), and then with each page refresh, those 6 products will change randomly.
Not my work by the way, so I can't take any credit.