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	$15.48	9.820%	$17.0001	$17.00	$17.00	$17.00
Purchase #2	$157.91	13.295%	$178.9041	$178.90	$178.90	$178.90
Purchase #3	$89.69	6.395%	$95.4257	$95.43	$95.45	$95.40
Purchase #4	$239.97	12.788%	$270.6574	$270.66	$270.65	$270.70
Purchase #5	$52.32	12.484%	$58.8516	$58.85	$58.85	$58.90
Purchase #6	$231.60	10.708%	$256.3997	$256.40	$256.40	$256.40
Purchase #7	$115.85	9.665%	$127.0469	$127.05	$127.05	$127.00
7 purchase totals =	$902.82		$1,004.2855	$1,004.29	$1,004.30	$1,004.30