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	$49.42	13.622%	$56.152	$56.15	$56.15	$56.20
Purchase #2	$154.65	11.392%	$172.2677	$172.27	$172.25	$172.30
Purchase #3	$91.71	6.491%	$97.6629	$97.66	$97.65	$97.70
Purchase #4	$144.98	7.272%	$155.5229	$155.52	$155.50	$155.50
Purchase #5	$31.51	7.362%	$33.8298	$33.83	$33.85	$33.80
Purchase #6	$156.55	12.263%	$175.7477	$175.75	$175.75	$175.70
Purchase #7	$88.98	7.330%	$95.5022	$95.50	$95.50	$95.50
7 purchase totals =	$717.80		$786.6852	$786.68	$786.65	$786.70