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	$24.72	10.177%	$27.2358	$27.24	$27.25	$27.20
Purchase #2	$112.65	4.345%	$117.5446	$117.54	$117.55	$117.50
Purchase #3	$107.28	5.658%	$113.3499	$113.35	$113.35	$113.30
Purchase #4	$17.61	6.554%	$18.7642	$18.76	$18.75	$18.80
Purchase #5	$16.83	6.862%	$17.9849	$17.98	$18.00	$18.00
Purchase #6	$103.72	7.106%	$111.0903	$111.09	$111.10	$111.10
Purchase #7	$144.47	13.762%	$164.352	$164.35	$164.35	$164.40
7 purchase totals =	$527.28		$570.3217	$570.31	$570.35	$570.30