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	$238.80	7.474%	$256.6479	$256.65	$256.65	$256.60
Purchase #2	$235.54	6.361%	$250.5227	$250.52	$250.50	$250.50
Purchase #3	$212.49	9.341%	$232.3387	$232.34	$232.35	$232.30
Purchase #4	$196.42	7.657%	$211.4599	$211.46	$211.45	$211.50
Purchase #5	$177.45	6.252%	$188.5442	$188.54	$188.55	$188.50
Purchase #6	$211.50	5.831%	$223.8326	$223.83	$223.85	$223.80
Purchase #7	$53.83	4.855%	$56.4434	$56.44	$56.45	$56.40
7 purchase totals =	$1,326.03		$1,419.7894	$1,419.78	$1,419.80	$1,419.60