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	$88.52	13.490%	$100.4613	$100.46	$100.45	$100.50
Purchase #2	$70.69	4.792%	$74.0775	$74.08	$74.10	$74.10
Purchase #3	$100.51	3.141%	$103.667	$103.67	$103.65	$103.70
Purchase #4	$74.43	4.392%	$77.699	$77.70	$77.70	$77.70
Purchase #5	$163.28	13.363%	$185.0991	$185.10	$185.10	$185.10
Purchase #6	$61.81	10.835%	$68.5071	$68.51	$68.50	$68.50
Purchase #7	$33.41	4.371%	$34.8704	$34.87	$34.85	$34.90
7 purchase totals =	$592.65		$644.3814	$644.39	$644.35	$644.50