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	$108.89	8.297%	$117.9246	$117.92	$117.90	$117.90
Purchase #2	$100.65	10.616%	$111.335	$111.34	$111.35	$111.30
Purchase #3	$18.34	11.836%	$20.5107	$20.51	$20.50	$20.50
Purchase #4	$48.88	12.755%	$55.1146	$55.11	$55.10	$55.10
Purchase #5	$61.92	10.613%	$68.4916	$68.49	$68.50	$68.50
Purchase #6	$147.63	7.312%	$158.4247	$158.42	$158.40	$158.40
Purchase #7	$141.64	5.171%	$148.9642	$148.96	$148.95	$149.00
7 purchase totals =	$627.95		$680.7654	$680.75	$680.70	$680.70