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	$104.95	6.608%	$111.8851	$111.89	$111.90	$111.90
Purchase #2	$140.67	11.342%	$156.6248	$156.62	$156.60	$156.60
Purchase #3	$220.29	13.509%	$250.049	$250.05	$250.05	$250.00
Purchase #4	$233.63	4.788%	$244.8162	$244.82	$244.80	$244.80
Purchase #5	$110.52	5.178%	$116.2427	$116.24	$116.25	$116.20
Purchase #6	$223.82	10.868%	$248.1448	$248.14	$248.15	$248.10
Purchase #7	$126.57	5.180%	$133.1263	$133.13	$133.15	$133.10
7 purchase totals =	$1,160.45		$1,260.8889	$1,260.89	$1,260.90	$1,260.70