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	$11.88	7.595%	$12.7823	$12.78	$12.80	$12.80
Purchase #2	$40.62	4.523%	$42.4572	$42.46	$42.45	$42.50
Purchase #3	$75.39	6.789%	$80.5082	$80.51	$80.50	$80.50
Purchase #4	$46.72	10.715%	$51.726	$51.73	$51.75	$51.70
Purchase #5	$85.27	4.479%	$89.0892	$89.09	$89.10	$89.10
Purchase #6	$205.94	8.718%	$223.8938	$223.89	$223.90	$223.90
Purchase #7	$15.40	13.720%	$17.5129	$17.51	$17.50	$17.50
7 purchase totals =	$481.22		$517.9696	$517.97	$518.00	$518.00