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	$111.84	5.622%	$118.1276	$118.13	$118.15	$118.10
Purchase #2	$131.85	11.358%	$146.8255	$146.83	$146.85	$146.80
Purchase #3	$46.32	12.650%	$52.1795	$52.18	$52.20	$52.20
Purchase #4	$179.67	8.473%	$194.8934	$194.89	$194.90	$194.90
Purchase #5	$242.29	4.686%	$253.6437	$253.64	$253.65	$253.60
Purchase #6	$178.66	6.677%	$190.5891	$190.59	$190.60	$190.60
Purchase #7	$5.91	8.360%	$6.4041	$6.40	$6.40	$6.40
7 purchase totals =	$896.54		$962.6629	$962.66	$962.75	$962.60