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	$59.37	9.778%	$65.1752	$65.18	$65.20	$65.20
Purchase #2	$250.63	4.770%	$262.5851	$262.59	$262.60	$262.60
Purchase #3	$42.90	8.303%	$46.462	$46.46	$46.45	$46.50
Purchase #4	$183.58	12.162%	$205.907	$205.91	$205.90	$205.90
Purchase #5	$14.43	3.258%	$14.9001	$14.90	$14.90	$14.90
Purchase #6	$139.46	10.604%	$154.2483	$154.25	$154.25	$154.20
Purchase #7	$104.70	6.280%	$111.2752	$111.28	$111.30	$111.30
7 purchase totals =	$795.07		$860.5529	$860.57	$860.60	$860.60