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	$122.83	4.346%	$128.1682	$128.17	$128.15	$128.20
Purchase #2	$56.95	8.663%	$61.8836	$61.88	$61.90	$61.90
Purchase #3	$174.79	12.345%	$196.3678	$196.37	$196.35	$196.40
Purchase #4	$219.42	7.834%	$236.6094	$236.61	$236.60	$236.60
Purchase #5	$37.67	13.353%	$42.7001	$42.70	$42.70	$42.70
Purchase #6	$143.52	7.114%	$153.73	$153.73	$153.75	$153.70
Purchase #7	$115.95	13.488%	$131.5893	$131.59	$131.60	$131.60
7 purchase totals =	$871.13		$951.0484	$951.05	$951.05	$951.10