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	$28.69	13.414%	$32.5385	$32.54	$32.55	$32.50
Purchase #2	$160.89	7.387%	$172.7749	$172.77	$172.75	$172.80
Purchase #3	$220.42	6.714%	$235.219	$235.22	$235.20	$235.20
Purchase #4	$100.49	7.650%	$108.1775	$108.18	$108.20	$108.20
Purchase #5	$159.82	4.758%	$167.4242	$167.42	$167.40	$167.40
Purchase #6	$6.54	13.443%	$7.4192	$7.42	$7.40	$7.40
Purchase #7	$48.97	11.564%	$54.6329	$54.63	$54.65	$54.60
7 purchase totals =	$725.82		$778.1862	$778.18	$778.15	$778.10