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	$140.27	4.307%	$146.3114	$146.31	$146.30	$146.30
Purchase #2	$222.30	7.338%	$238.6124	$238.61	$238.60	$238.60
Purchase #3	$100.73	12.337%	$113.1571	$113.16	$113.15	$113.20
Purchase #4	$44.77	5.375%	$47.1764	$47.18	$47.20	$47.20
Purchase #5	$139.92	10.780%	$155.0034	$155.00	$155.00	$155.00
Purchase #6	$106.31	6.693%	$113.4253	$113.43	$113.45	$113.40
Purchase #7	$232.56	9.820%	$255.3974	$255.40	$255.40	$255.40
7 purchase totals =	$986.86		$1,069.0834	$1,069.09	$1,069.10	$1,069.10