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	$93.42	13.357%	$105.8981	$105.90	$105.90	$105.90
Purchase #2	$137.32	12.414%	$154.3669	$154.37	$154.35	$154.40
Purchase #3	$15.82	13.767%	$17.9979	$18.00	$18.00	$18.00
Purchase #4	$247.94	12.594%	$279.1656	$279.17	$279.15	$279.20
Purchase #5	$160.45	6.732%	$171.2515	$171.25	$171.25	$171.30
Purchase #6	$11.30	3.390%	$11.6831	$11.68	$11.70	$11.70
Purchase #7	$17.36	5.634%	$18.3381	$18.34	$18.35	$18.30
7 purchase totals =	$683.61		$758.7012	$758.71	$758.70	$758.80