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	$86.39	3.301%	$89.2417	$89.24	$89.25	$89.20
Purchase #2	$119.96	10.338%	$132.3615	$132.36	$132.35	$132.40
Purchase #3	$82.39	8.757%	$89.6049	$89.60	$89.60	$89.60
Purchase #4	$105.68	13.459%	$119.9035	$119.90	$119.90	$119.90
Purchase #5	$21.85	12.519%	$24.5854	$24.59	$24.60	$24.60
Purchase #6	$59.71	10.855%	$66.1915	$66.19	$66.20	$66.20
Purchase #7	$21.65	4.841%	$22.6981	$22.70	$22.70	$22.70
7 purchase totals =	$497.63		$544.5866	$544.58	$544.60	$544.60