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	$10.78	6.813%	$11.5144	$11.51	$11.50	$11.50
Purchase #2	$54.70	3.367%	$56.5417	$56.54	$56.55	$56.50
Purchase #3	$139.35	4.453%	$145.5553	$145.56	$145.55	$145.60
Purchase #4	$44.42	13.870%	$50.5811	$50.58	$50.60	$50.60
Purchase #5	$14.35	7.177%	$15.3799	$15.38	$15.40	$15.40
Purchase #6	$194.49	11.688%	$217.222	$217.22	$217.20	$217.20
Purchase #7	$40.43	12.459%	$45.4672	$45.47	$45.45	$45.50
7 purchase totals =	$498.52		$542.2616	$542.26	$542.25	$542.30