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	$86.78	4.643%	$90.8092	$90.81	$90.80	$90.80
Purchase #2	$142.58	6.626%	$152.0274	$152.03	$152.05	$152.00
Purchase #3	$49.46	10.616%	$54.7107	$54.71	$54.70	$54.70
Purchase #4	$39.77	4.516%	$41.566	$41.57	$41.55	$41.60
Purchase #5	$25.95	6.251%	$27.5721	$27.57	$27.55	$27.60
Purchase #6	$6.37	6.733%	$6.7989	$6.80	$6.80	$6.80
Purchase #7	$178.54	7.479%	$191.893	$191.89	$191.90	$191.90
7 purchase totals =	$529.45		$565.3773	$565.38	$565.35	$565.40