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	$27.52	13.625%	$31.2696	$31.27	$31.25	$31.30
Purchase #2	$224.59	6.189%	$238.4899	$238.49	$238.50	$238.50
Purchase #3	$177.50	11.745%	$198.3474	$198.35	$198.35	$198.30
Purchase #4	$161.77	7.338%	$173.6407	$173.64	$173.65	$173.60
Purchase #5	$238.25	8.348%	$258.1391	$258.14	$258.15	$258.10
Purchase #6	$74.27	8.599%	$80.6565	$80.66	$80.65	$80.70
Purchase #7	$32.87	7.781%	$35.4276	$35.43	$35.45	$35.40
7 purchase totals =	$936.77		$1,015.9708	$1,015.98	$1,016.00	$1,015.90