If you want to tweak how the total amount is displayed in the simple shopping cart then open the "wp_shopping_cart.php" file and look for the following function:
function print_payment_currency($price, $symbol, $decimal)
{
return $symbol.number_format($price, 2, $decimal, ',');
}This is the function that displayed the amount to two decimal places. Tweak it to however you want to display your price amount.