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	$128.50	8.726%	$139.7129	$139.71	$139.70	$139.70
Purchase #2	$205.78	12.105%	$230.6897	$230.69	$230.70	$230.70
Purchase #3	$106.43	7.862%	$114.7975	$114.80	$114.80	$114.80
Purchase #4	$148.65	10.406%	$164.1185	$164.12	$164.10	$164.10
Purchase #5	$90.37	9.658%	$99.0979	$99.10	$99.10	$99.10
Purchase #6	$97.60	7.741%	$105.1552	$105.16	$105.15	$105.20
Purchase #7	$228.71	3.335%	$236.3375	$236.34	$236.35	$236.30
7 purchase totals =	$1,006.04		$1,089.9092	$1,089.92	$1,089.90	$1,089.90