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	$241.45	3.548%	$250.0166	$250.02	$250.00	$250.00
Purchase #2	$65.33	7.563%	$70.2709	$70.27	$70.25	$70.30
Purchase #3	$117.80	4.810%	$123.4662	$123.47	$123.45	$123.50
Purchase #4	$205.94	4.103%	$214.3897	$214.39	$214.40	$214.40
Purchase #5	$41.81	12.150%	$46.8899	$46.89	$46.90	$46.90
Purchase #6	$18.27	4.685%	$19.1259	$19.13	$19.15	$19.10
Purchase #7	$166.92	10.128%	$183.8257	$183.83	$183.85	$183.80
7 purchase totals =	$857.52		$907.9849	$908.00	$908.00	$908.00