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	$75.74	5.729%	$80.0791	$80.08	$80.10	$80.10
Purchase #2	$232.78	12.325%	$261.4701	$261.47	$261.45	$261.50
Purchase #3	$248.81	5.540%	$262.5941	$262.59	$262.60	$262.60
Purchase #4	$105.69	10.160%	$116.4281	$116.43	$116.45	$116.40
Purchase #5	$116.76	13.503%	$132.5261	$132.53	$132.55	$132.50
Purchase #6	$38.85	3.453%	$40.1915	$40.19	$40.20	$40.20
Purchase #7	$132.85	3.569%	$137.5914	$137.59	$137.60	$137.60
7 purchase totals =	$951.48		$1,030.8804	$1,030.88	$1,030.95	$1,030.90