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	$68.77	8.303%	$74.48	$74.48	$74.50	$74.50
Purchase #2	$97.25	6.739%	$103.8037	$103.80	$103.80	$103.80
Purchase #3	$10.48	4.291%	$10.9297	$10.93	$10.95	$10.90
Purchase #4	$87.43	13.603%	$99.3231	$99.32	$99.30	$99.30
Purchase #5	$122.47	7.198%	$131.2854	$131.29	$131.30	$131.30
Purchase #6	$46.30	9.773%	$50.8249	$50.82	$50.80	$50.80
Purchase #7	$36.34	5.730%	$38.4223	$38.42	$38.40	$38.40
7 purchase totals =	$469.04		$509.0691	$509.06	$509.05	$509.00