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	$15.87	7.726%	$17.0961	$17.10	$17.10	$17.10
Purchase #2	$243.83	4.700%	$255.29	$255.29	$255.30	$255.30
Purchase #3	$114.87	6.324%	$122.1344	$122.13	$122.15	$122.10
Purchase #4	$128.56	12.355%	$144.4436	$144.44	$144.45	$144.40
Purchase #5	$57.85	13.386%	$65.5938	$65.59	$65.60	$65.60
Purchase #6	$45.40	13.627%	$51.5867	$51.59	$51.60	$51.60
Purchase #7	$235.77	8.853%	$256.6427	$256.64	$256.65	$256.60
7 purchase totals =	$842.15		$912.7873	$912.78	$912.85	$912.70