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	$30.55	9.726%	$33.5213	$33.52	$33.50	$33.50
Purchase #2	$75.94	3.540%	$78.6283	$78.63	$78.65	$78.60
Purchase #3	$31.60	13.311%	$35.8063	$35.81	$35.80	$35.80
Purchase #4	$237.57	7.590%	$255.6016	$255.60	$255.60	$255.60
Purchase #5	$217.61	10.257%	$239.9303	$239.93	$239.95	$239.90
Purchase #6	$105.93	5.468%	$111.7223	$111.72	$111.70	$111.70
Purchase #7	$14.51	12.796%	$16.3667	$16.37	$16.35	$16.40
7 purchase totals =	$713.71		$771.5768	$771.58	$771.55	$771.50