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	$144.69	11.239%	$160.9517	$160.95	$160.95	$161.00
Purchase #2	$54.77	13.718%	$62.2833	$62.28	$62.30	$62.30
Purchase #3	$46.56	10.808%	$51.5922	$51.59	$51.60	$51.60
Purchase #4	$11.94	5.149%	$12.5548	$12.55	$12.55	$12.60
Purchase #5	$129.87	7.294%	$139.3427	$139.34	$139.35	$139.30
Purchase #6	$34.59	8.835%	$37.646	$37.65	$37.65	$37.60
Purchase #7	$146.43	3.841%	$152.0544	$152.05	$152.05	$152.10
7 purchase totals =	$568.85		$616.4251	$616.41	$616.45	$616.50