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	$230.98	7.104%	$247.3888	$247.39	$247.40	$247.40
Purchase #2	$29.27	11.789%	$32.7206	$32.72	$32.70	$32.70
Purchase #3	$100.76	3.436%	$104.2221	$104.22	$104.20	$104.20
Purchase #4	$143.85	10.633%	$159.1456	$159.15	$159.15	$159.10
Purchase #5	$93.98	6.242%	$99.8462	$99.85	$99.85	$99.80
Purchase #6	$48.32	8.776%	$52.5606	$52.56	$52.55	$52.60
Purchase #7	$167.90	3.311%	$173.4592	$173.46	$173.45	$173.50
7 purchase totals =	$815.06		$869.3431	$869.35	$869.30	$869.30