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	$34.70	13.730%	$39.4643	$39.46	$39.45	$39.50
Purchase #2	$54.81	13.163%	$62.0246	$62.02	$62.00	$62.00
Purchase #3	$219.27	6.486%	$233.4919	$233.49	$233.50	$233.50
Purchase #4	$112.80	13.265%	$127.7629	$127.76	$127.75	$127.80
Purchase #5	$87.48	11.816%	$97.8166	$97.82	$97.80	$97.80
Purchase #6	$137.90	5.273%	$145.1715	$145.17	$145.15	$145.20
Purchase #7	$232.60	11.376%	$259.0606	$259.06	$259.05	$259.10
7 purchase totals =	$879.56		$964.7924	$964.78	$964.70	$964.90