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	$231.38	10.430%	$255.5129	$255.51	$255.50	$255.50
Purchase #2	$242.68	5.652%	$256.3963	$256.40	$256.40	$256.40
Purchase #3	$232.93	10.595%	$257.6089	$257.61	$257.60	$257.60
Purchase #4	$43.77	4.538%	$45.7563	$45.76	$45.75	$45.80
Purchase #5	$46.27	13.433%	$52.4854	$52.49	$52.50	$52.50
Purchase #6	$137.32	10.496%	$151.7331	$151.73	$151.75	$151.70
Purchase #7	$53.26	5.346%	$56.1073	$56.11	$56.10	$56.10
7 purchase totals =	$987.61		$1,075.6002	$1,075.61	$1,075.60	$1,075.60