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	$53.54	6.762%	$57.1604	$57.16	$57.15	$57.20
Purchase #2	$72.95	4.388%	$76.151	$76.15	$76.15	$76.20
Purchase #3	$105.58	7.311%	$113.299	$113.30	$113.30	$113.30
Purchase #4	$183.56	13.787%	$208.8674	$208.87	$208.85	$208.90
Purchase #5	$34.39	11.634%	$38.3909	$38.39	$38.40	$38.40
Purchase #6	$227.52	11.315%	$253.2639	$253.26	$253.25	$253.30
Purchase #7	$185.28	3.174%	$191.1608	$191.16	$191.15	$191.20
7 purchase totals =	$862.82		$938.2934	$938.29	$938.25	$938.50