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	$33.57	10.538%	$37.1076	$37.11	$37.10	$37.10
Purchase #2	$60.61	3.225%	$62.5647	$62.56	$62.55	$62.60
Purchase #3	$106.71	4.277%	$111.274	$111.27	$111.25	$111.30
Purchase #4	$129.47	8.192%	$140.0762	$140.08	$140.10	$140.10
Purchase #5	$16.91	4.563%	$17.6816	$17.68	$17.70	$17.70
Purchase #6	$125.29	7.174%	$134.2783	$134.28	$134.30	$134.30
Purchase #7	$6.86	4.480%	$7.1673	$7.17	$7.15	$7.20
7 purchase totals =	$479.42		$510.1497	$510.15	$510.15	$510.30