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	$178.67	3.383%	$184.7144	$184.71	$184.70	$184.70
Purchase #2	$222.47	7.191%	$238.4678	$238.47	$238.45	$238.50
Purchase #3	$111.56	5.243%	$117.4091	$117.41	$117.40	$117.40
Purchase #4	$13.90	13.697%	$15.8039	$15.80	$15.80	$15.80
Purchase #5	$37.40	11.639%	$41.753	$41.75	$41.75	$41.80
Purchase #6	$143.35	13.113%	$162.1475	$162.15	$162.15	$162.10
Purchase #7	$35.44	6.673%	$37.8049	$37.80	$37.80	$37.80
7 purchase totals =	$742.79		$798.1006	$798.09	$798.05	$798.10