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	$142.60	12.204%	$160.0029	$160.00	$160.00	$160.00
Purchase #2	$28.81	13.569%	$32.7192	$32.72	$32.70	$32.70
Purchase #3	$105.39	11.104%	$117.0925	$117.09	$117.10	$117.10
Purchase #4	$95.72	10.702%	$105.964	$105.96	$105.95	$106.00
Purchase #5	$38.75	13.132%	$43.8387	$43.84	$43.85	$43.80
Purchase #6	$107.88	8.250%	$116.7801	$116.78	$116.80	$116.80
Purchase #7	$38.59	11.619%	$43.0738	$43.07	$43.05	$43.10
7 purchase totals =	$557.74		$619.4712	$619.46	$619.45	$619.50