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	$250.31	12.325%	$281.1607	$281.16	$281.15	$281.20
Purchase #2	$42.96	7.769%	$46.2976	$46.30	$46.30	$46.30
Purchase #3	$40.28	5.829%	$42.6279	$42.63	$42.65	$42.60
Purchase #4	$28.83	8.449%	$31.2658	$31.27	$31.25	$31.30
Purchase #5	$208.42	4.668%	$218.149	$218.15	$218.15	$218.10
Purchase #6	$141.47	9.401%	$154.7696	$154.77	$154.75	$154.80
Purchase #7	$116.77	10.180%	$128.6572	$128.66	$128.65	$128.70
7 purchase totals =	$829.04		$902.9278	$902.94	$902.90	$903.00