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	$9.98	6.808%	$10.6594	$10.66	$10.65	$10.70
Purchase #2	$35.52	5.821%	$37.5876	$37.59	$37.60	$37.60
Purchase #3	$150.83	4.627%	$157.8089	$157.81	$157.80	$157.80
Purchase #4	$19.62	3.583%	$20.323	$20.32	$20.30	$20.30
Purchase #5	$230.72	11.323%	$256.8444	$256.84	$256.85	$256.80
Purchase #6	$152.77	11.180%	$169.8497	$169.85	$169.85	$169.80
Purchase #7	$13.85	4.525%	$14.4767	$14.48	$14.50	$14.50
7 purchase totals =	$613.29		$667.5497	$667.55	$667.55	$667.50