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	$9.97	8.538%	$10.8212	$10.82	$10.80	$10.80
Purchase #2	$234.96	6.303%	$249.7695	$249.77	$249.75	$249.80
Purchase #3	$46.49	7.689%	$50.0646	$50.06	$50.05	$50.10
Purchase #4	$148.99	4.368%	$155.4979	$155.50	$155.50	$155.50
Purchase #5	$225.35	8.103%	$243.6101	$243.61	$243.60	$243.60
Purchase #6	$55.72	10.566%	$61.6074	$61.61	$61.60	$61.60
Purchase #7	$95.56	3.476%	$98.8817	$98.88	$98.90	$98.90
7 purchase totals =	$817.04		$870.2524	$870.25	$870.20	$870.30