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	$236.27	10.798%	$261.7824	$261.78	$261.80	$261.80
Purchase #2	$86.84	3.859%	$90.1912	$90.19	$90.20	$90.20
Purchase #3	$10.85	9.613%	$11.893	$11.89	$11.90	$11.90
Purchase #4	$72.71	11.201%	$80.8542	$80.85	$80.85	$80.90
Purchase #5	$100.25	3.193%	$103.451	$103.45	$103.45	$103.50
Purchase #6	$30.40	5.334%	$32.0215	$32.02	$32.00	$32.00
Purchase #7	$17.39	10.162%	$19.1572	$19.16	$19.15	$19.20
7 purchase totals =	$554.71		$599.3505	$599.34	$599.35	$599.50