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	$45.59	5.645%	$48.1636	$48.16	$48.15	$48.20
Purchase #2	$190.75	3.233%	$196.9169	$196.92	$196.90	$196.90
Purchase #3	$152.78	12.860%	$172.4275	$172.43	$172.45	$172.40
Purchase #4	$205.34	8.680%	$223.1635	$223.16	$223.15	$223.20
Purchase #5	$42.86	10.736%	$47.4614	$47.46	$47.45	$47.50
Purchase #6	$121.80	4.635%	$127.4454	$127.45	$127.45	$127.40
Purchase #7	$16.31	10.492%	$18.0212	$18.02	$18.00	$18.00
7 purchase totals =	$775.43		$833.5995	$833.60	$833.55	$833.60