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	$51.62	3.595%	$53.4757	$53.48	$53.50	$53.50
Purchase #2	$83.30	8.468%	$90.3538	$90.35	$90.35	$90.40
Purchase #3	$11.82	10.501%	$13.0612	$13.06	$13.05	$13.10
Purchase #4	$32.98	8.555%	$35.8014	$35.80	$35.80	$35.80
Purchase #5	$30.72	11.303%	$34.1923	$34.19	$34.20	$34.20
Purchase #6	$250.97	11.297%	$279.3221	$279.32	$279.30	$279.30
Purchase #7	$184.78	3.145%	$190.5913	$190.59	$190.60	$190.60
7 purchase totals =	$646.19		$696.7978	$696.79	$696.80	$696.90