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	$15.99	10.379%	$17.6496	$17.65	$17.65	$17.60
Purchase #2	$77.65	5.786%	$82.1428	$82.14	$82.15	$82.10
Purchase #3	$42.81	6.514%	$45.5986	$45.60	$45.60	$45.60
Purchase #4	$188.60	11.276%	$209.8665	$209.87	$209.85	$209.90
Purchase #5	$221.60	13.650%	$251.8484	$251.85	$251.85	$251.80
Purchase #6	$100.95	4.433%	$105.4251	$105.43	$105.45	$105.40
Purchase #7	$199.71	10.602%	$220.8833	$220.88	$220.90	$220.90
7 purchase totals =	$847.31		$933.4143	$933.42	$933.45	$933.30