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	$105.57	12.455%	$118.7187	$118.72	$118.70	$118.70
Purchase #2	$74.61	3.859%	$77.4892	$77.49	$77.50	$77.50
Purchase #3	$215.30	12.335%	$241.8573	$241.86	$241.85	$241.90
Purchase #4	$75.29	6.852%	$80.4489	$80.45	$80.45	$80.40
Purchase #5	$64.54	10.492%	$71.3115	$71.31	$71.30	$71.30
Purchase #6	$214.88	3.125%	$221.595	$221.60	$221.60	$221.60
Purchase #7	$88.39	12.512%	$99.4494	$99.45	$99.45	$99.40
7 purchase totals =	$838.58		$910.8700	$910.88	$910.85	$910.80