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	$217.91	11.376%	$242.6994	$242.70	$242.70	$242.70
Purchase #2	$121.34	6.128%	$128.7757	$128.78	$128.80	$128.80
Purchase #3	$167.25	3.867%	$173.7176	$173.72	$173.70	$173.70
Purchase #4	$182.28	12.714%	$205.4551	$205.46	$205.45	$205.50
Purchase #5	$18.53	9.303%	$20.2538	$20.25	$20.25	$20.30
Purchase #6	$160.39	3.791%	$166.4704	$166.47	$166.45	$166.50
Purchase #7	$22.69	10.191%	$25.0023	$25.00	$25.00	$25.00
7 purchase totals =	$890.39		$962.3743	$962.38	$962.35	$962.50