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	$102.89	8.164%	$111.2899	$111.29	$111.30	$111.30
Purchase #2	$49.70	5.187%	$52.2779	$52.28	$52.30	$52.30
Purchase #3	$138.92	3.134%	$143.2738	$143.27	$143.25	$143.30
Purchase #4	$147.98	6.520%	$157.6283	$157.63	$157.65	$157.60
Purchase #5	$7.85	8.482%	$8.5158	$8.52	$8.50	$8.50
Purchase #6	$124.42	13.442%	$141.1445	$141.14	$141.15	$141.10
Purchase #7	$37.77	7.449%	$40.5835	$40.58	$40.60	$40.60
7 purchase totals =	$609.53		$654.7137	$654.71	$654.75	$654.70