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	$11.74	13.117%	$13.2799	$13.28	$13.30	$13.30
Purchase #2	$47.89	12.381%	$53.8193	$53.82	$53.80	$53.80
Purchase #3	$94.44	6.657%	$100.7269	$100.73	$100.75	$100.70
Purchase #4	$46.53	7.675%	$50.1012	$50.10	$50.10	$50.10
Purchase #5	$244.51	11.514%	$272.6629	$272.66	$272.65	$272.70
Purchase #6	$56.72	10.670%	$62.772	$62.77	$62.75	$62.80
Purchase #7	$65.27	10.197%	$71.9256	$71.93	$71.95	$71.90
7 purchase totals =	$567.10		$625.2878	$625.29	$625.30	$625.30