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	$83.56	6.290%	$88.8159	$88.82	$88.80	$88.80
Purchase #2	$35.57	12.103%	$39.875	$39.88	$39.90	$39.90
Purchase #3	$45.99	13.671%	$52.2773	$52.28	$52.30	$52.30
Purchase #4	$230.57	8.674%	$250.5696	$250.57	$250.55	$250.60
Purchase #5	$7.56	10.516%	$8.355	$8.36	$8.35	$8.40
Purchase #6	$112.76	3.304%	$116.4856	$116.49	$116.50	$116.50
Purchase #7	$88.72	13.561%	$100.7513	$100.75	$100.75	$100.80
7 purchase totals =	$604.73		$657.1297	$657.15	$657.15	$657.30