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	$28.71	13.531%	$32.5948	$32.59	$32.60	$32.60
Purchase #2	$91.85	13.142%	$103.9209	$103.92	$103.90	$103.90
Purchase #3	$136.69	8.332%	$148.079	$148.08	$148.10	$148.10
Purchase #4	$13.49	13.718%	$15.3406	$15.34	$15.35	$15.30
Purchase #5	$240.43	12.127%	$269.5869	$269.59	$269.60	$269.60
Purchase #6	$134.48	8.341%	$145.697	$145.70	$145.70	$145.70
Purchase #7	$224.57	6.693%	$239.6005	$239.60	$239.60	$239.60
7 purchase totals =	$870.22		$954.8197	$954.82	$954.85	$954.80