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	$18.45	10.503%	$20.3878	$20.39	$20.40	$20.40
Purchase #2	$146.73	9.827%	$161.1492	$161.15	$161.15	$161.10
Purchase #3	$66.94	9.771%	$73.4807	$73.48	$73.50	$73.50
Purchase #4	$189.83	13.699%	$215.8348	$215.83	$215.85	$215.80
Purchase #5	$30.60	12.311%	$34.3672	$34.37	$34.35	$34.40
Purchase #6	$30.85	7.412%	$33.1366	$33.14	$33.15	$33.10
Purchase #7	$49.63	7.342%	$53.2738	$53.27	$53.25	$53.30
7 purchase totals =	$533.03		$591.6301	$591.63	$591.65	$591.60