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	$150.87	10.142%	$166.1712	$166.17	$166.15	$166.20
Purchase #2	$232.91	6.245%	$247.4552	$247.46	$247.45	$247.50
Purchase #3	$107.39	10.172%	$118.3137	$118.31	$118.30	$118.30
Purchase #4	$37.27	6.239%	$39.5953	$39.60	$39.60	$39.60
Purchase #5	$50.95	13.584%	$57.871	$57.87	$57.85	$57.90
Purchase #6	$37.94	9.175%	$41.421	$41.42	$41.40	$41.40
Purchase #7	$241.77	8.544%	$262.4268	$262.43	$262.45	$262.40
7 purchase totals =	$859.10		$933.2542	$933.26	$933.20	$933.30