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	$32.25	7.865%	$34.7865	$34.79	$34.80	$34.80
Purchase #2	$52.34	3.306%	$54.0704	$54.07	$54.05	$54.10
Purchase #3	$133.36	10.140%	$146.8827	$146.88	$146.90	$146.90
Purchase #4	$198.89	13.435%	$225.6109	$225.61	$225.60	$225.60
Purchase #5	$48.52	12.378%	$54.5258	$54.53	$54.55	$54.50
Purchase #6	$187.82	4.141%	$195.5976	$195.60	$195.60	$195.60
Purchase #7	$143.85	9.453%	$157.4481	$157.45	$157.45	$157.40
7 purchase totals =	$797.03		$868.9220	$868.93	$868.95	$868.90