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	$105.28	5.823%	$111.4105	$111.41	$111.40	$111.40
Purchase #2	$75.73	13.721%	$86.1209	$86.12	$86.10	$86.10
Purchase #3	$103.53	11.745%	$115.6896	$115.69	$115.70	$115.70
Purchase #4	$224.31	5.446%	$236.5259	$236.53	$236.55	$236.50
Purchase #5	$19.73	3.749%	$20.4697	$20.47	$20.45	$20.50
Purchase #6	$46.83	4.699%	$49.0305	$49.03	$49.05	$49.00
Purchase #7	$42.26	11.389%	$47.073	$47.07	$47.05	$47.10
7 purchase totals =	$617.67		$666.3201	$666.32	$666.30	$666.30