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	$48.66	4.531%	$50.8648	$50.86	$50.85	$50.90
Purchase #2	$199.81	13.845%	$227.4737	$227.47	$227.45	$227.50
Purchase #3	$192.58	10.292%	$212.4003	$212.40	$212.40	$212.40
Purchase #4	$126.54	13.396%	$143.4913	$143.49	$143.50	$143.50
Purchase #5	$244.43	5.174%	$257.0768	$257.08	$257.10	$257.10
Purchase #6	$127.46	3.269%	$131.6267	$131.63	$131.65	$131.60
Purchase #7	$58.79	4.351%	$61.348	$61.35	$61.35	$61.30
7 purchase totals =	$998.27		$1,084.2816	$1,084.28	$1,084.30	$1,084.30