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	$39.93	9.456%	$43.7058	$43.71	$43.70	$43.70
Purchase #2	$178.65	12.302%	$200.6275	$200.63	$200.65	$200.60
Purchase #3	$152.66	13.367%	$173.0661	$173.07	$173.05	$173.10
Purchase #4	$51.78	4.714%	$54.2209	$54.22	$54.20	$54.20
Purchase #5	$72.50	8.581%	$78.7212	$78.72	$78.70	$78.70
Purchase #6	$18.85	9.628%	$20.6649	$20.66	$20.65	$20.70
Purchase #7	$248.82	9.556%	$272.5972	$272.60	$272.60	$272.60
7 purchase totals =	$763.19		$843.6036	$843.61	$843.55	$843.60