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	$38.50	5.267%	$40.5278	$40.53	$40.55	$40.50
Purchase #2	$104.52	12.354%	$117.4324	$117.43	$117.45	$117.40
Purchase #3	$183.39	6.145%	$194.6593	$194.66	$194.65	$194.70
Purchase #4	$228.34	11.784%	$255.2476	$255.25	$255.25	$255.20
Purchase #5	$88.29	13.372%	$100.0961	$100.10	$100.10	$100.10
Purchase #6	$19.37	7.760%	$20.8731	$20.87	$20.85	$20.90
Purchase #7	$124.77	10.336%	$137.6662	$137.67	$137.65	$137.70
7 purchase totals =	$787.18		$866.5025	$866.51	$866.50	$866.50