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	$94.58	6.251%	$100.4922	$100.49	$100.50	$100.50
Purchase #2	$159.84	11.809%	$178.7155	$178.72	$178.70	$178.70
Purchase #3	$57.89	8.210%	$62.6428	$62.64	$62.65	$62.60
Purchase #4	$177.90	4.498%	$185.9019	$185.90	$185.90	$185.90
Purchase #5	$34.35	7.845%	$37.0448	$37.04	$37.05	$37.00
Purchase #6	$168.83	10.660%	$186.8273	$186.83	$186.85	$186.80
Purchase #7	$146.49	8.511%	$158.9578	$158.96	$158.95	$159.00
7 purchase totals =	$839.88		$910.5823	$910.58	$910.60	$910.50