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	$94.27	6.118%	$100.0374	$100.04	$100.05	$100.00
Purchase #2	$80.42	4.383%	$83.9448	$83.94	$83.95	$83.90
Purchase #3	$218.34	12.162%	$244.8945	$244.89	$244.90	$244.90
Purchase #4	$118.66	7.683%	$127.7766	$127.78	$127.80	$127.80
Purchase #5	$77.29	3.198%	$79.7617	$79.76	$79.75	$79.80
Purchase #6	$244.40	3.831%	$253.763	$253.76	$253.75	$253.80
Purchase #7	$6.53	3.847%	$6.7812	$6.78	$6.80	$6.80
7 purchase totals =	$839.91		$896.9592	$896.95	$897.00	$897.00