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	$37.65	13.571%	$42.7595	$42.76	$42.75	$42.80
Purchase #2	$26.89	3.820%	$27.9172	$27.92	$27.90	$27.90
Purchase #3	$99.40	5.479%	$104.8461	$104.85	$104.85	$104.80
Purchase #4	$87.27	4.186%	$90.9231	$90.92	$90.90	$90.90
Purchase #5	$223.48	12.768%	$252.0139	$252.01	$252.00	$252.00
Purchase #6	$145.59	4.754%	$152.5113	$152.51	$152.50	$152.50
Purchase #7	$51.64	10.680%	$57.1552	$57.16	$57.15	$57.20
7 purchase totals =	$671.92		$728.1263	$728.13	$728.05	$728.10