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	$118.45	12.396%	$133.1331	$133.13	$133.15	$133.10
Purchase #2	$46.87	5.710%	$49.5463	$49.55	$49.55	$49.50
Purchase #3	$200.52	12.772%	$226.1304	$226.13	$226.15	$226.10
Purchase #4	$129.87	11.852%	$145.2622	$145.26	$145.25	$145.30
Purchase #5	$234.77	8.805%	$255.4415	$255.44	$255.45	$255.40
Purchase #6	$215.65	3.640%	$223.4997	$223.50	$223.50	$223.50
Purchase #7	$249.35	10.575%	$275.7188	$275.72	$275.70	$275.70
7 purchase totals =	$1,195.48		$1,308.7320	$1,308.73	$1,308.75	$1,308.60