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	$157.27	3.526%	$162.8153	$162.82	$162.80	$162.80
Purchase #2	$241.73	11.649%	$269.8891	$269.89	$269.90	$269.90
Purchase #3	$212.86	11.312%	$236.9387	$236.94	$236.95	$236.90
Purchase #4	$48.69	7.523%	$52.3529	$52.35	$52.35	$52.40
Purchase #5	$212.72	5.248%	$223.8835	$223.88	$223.90	$223.90
Purchase #6	$175.52	8.147%	$189.8196	$189.82	$189.80	$189.80
Purchase #7	$143.84	3.516%	$148.8974	$148.90	$148.90	$148.90
7 purchase totals =	$1,192.63		$1,284.5965	$1,284.60	$1,284.60	$1,284.60