Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$225.70	6.465%	$240.2915	$240.29	$240.30	$240.30
Purchase #2	$105.38	13.697%	$119.8139	$119.81	$119.80	$119.80
Purchase #3	$39.71	4.204%	$41.3794	$41.38	$41.40	$41.40
Purchase #4	$233.55	12.209%	$262.0641	$262.06	$262.05	$262.10
Purchase #5	$126.53	12.298%	$142.0907	$142.09	$142.10	$142.10
Purchase #6	$28.35	10.261%	$31.259	$31.26	$31.25	$31.30
Purchase #7	$48.61	10.507%	$53.7175	$53.72	$53.70	$53.70
7 purchase totals =	$807.83		$890.6161	$890.61	$890.60	$890.70