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	$181.64	10.584%	$200.8648	$200.86	$200.85	$200.90
Purchase #2	$52.61	8.772%	$57.2249	$57.22	$57.20	$57.20
Purchase #3	$53.60	9.630%	$58.7617	$58.76	$58.75	$58.80
Purchase #4	$59.34	5.126%	$62.3818	$62.38	$62.40	$62.40
Purchase #5	$86.45	4.233%	$90.1094	$90.11	$90.10	$90.10
Purchase #6	$19.30	13.487%	$21.903	$21.90	$21.90	$21.90
Purchase #7	$136.25	13.303%	$154.3753	$154.38	$154.40	$154.40
7 purchase totals =	$589.19		$645.6209	$645.61	$645.60	$645.70