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	$40.83	4.549%	$42.6874	$42.69	$42.70	$42.70
Purchase #2	$74.29	12.826%	$83.8184	$83.82	$83.80	$83.80
Purchase #3	$33.40	10.830%	$37.0172	$37.02	$37.00	$37.00
Purchase #4	$183.45	11.717%	$204.9448	$204.94	$204.95	$204.90
Purchase #5	$126.68	8.819%	$137.8519	$137.85	$137.85	$137.90
Purchase #6	$126.76	11.550%	$141.4008	$141.40	$141.40	$141.40
Purchase #7	$122.38	9.395%	$133.8776	$133.88	$133.90	$133.90
7 purchase totals =	$707.79		$781.5981	$781.60	$781.60	$781.60