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	$165.53	6.637%	$176.5162	$176.52	$176.50	$176.50
Purchase #2	$247.93	5.527%	$261.6331	$261.63	$261.65	$261.60
Purchase #3	$116.84	12.646%	$131.6156	$131.62	$131.60	$131.60
Purchase #4	$108.71	13.482%	$123.3663	$123.37	$123.35	$123.40
Purchase #5	$30.61	5.680%	$32.3486	$32.35	$32.35	$32.30
Purchase #6	$23.32	11.247%	$25.9428	$25.94	$25.95	$25.90
Purchase #7	$137.84	6.533%	$146.8451	$146.85	$146.85	$146.80
7 purchase totals =	$830.78		$898.2677	$898.28	$898.25	$898.10