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	$122.54	5.215%	$128.9305	$128.93	$128.95	$128.90
Purchase #2	$39.35	3.781%	$40.8378	$40.84	$40.85	$40.80
Purchase #3	$61.52	8.795%	$66.9307	$66.93	$66.95	$66.90
Purchase #4	$155.82	6.678%	$166.2257	$166.23	$166.25	$166.20
Purchase #5	$127.88	4.296%	$133.3737	$133.37	$133.35	$133.40
Purchase #6	$130.31	10.857%	$144.4578	$144.46	$144.45	$144.50
Purchase #7	$247.94	4.381%	$258.8023	$258.80	$258.80	$258.80
7 purchase totals =	$885.36		$939.5585	$939.56	$939.60	$939.50