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	$100.56	8.109%	$108.7144	$108.71	$108.70	$108.70
Purchase #2	$166.68	12.873%	$188.1367	$188.14	$188.15	$188.10
Purchase #3	$119.46	12.852%	$134.813	$134.81	$134.80	$134.80
Purchase #4	$132.68	13.573%	$150.6887	$150.69	$150.70	$150.70
Purchase #5	$74.94	10.383%	$82.721	$82.72	$82.70	$82.70
Purchase #6	$138.51	8.375%	$150.1102	$150.11	$150.10	$150.10
Purchase #7	$87.26	3.248%	$90.0942	$90.09	$90.10	$90.10
7 purchase totals =	$820.09		$905.2782	$905.27	$905.25	$905.20