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	$10.71	4.859%	$11.2304	$11.23	$11.25	$11.20
Purchase #2	$59.50	12.335%	$66.8393	$66.84	$66.85	$66.80
Purchase #3	$208.64	8.379%	$226.1219	$226.12	$226.10	$226.10
Purchase #4	$235.58	8.558%	$255.7409	$255.74	$255.75	$255.70
Purchase #5	$155.70	10.866%	$172.6184	$172.62	$172.60	$172.60
Purchase #6	$96.85	6.598%	$103.2402	$103.24	$103.25	$103.20
Purchase #7	$59.83	6.759%	$63.8739	$63.87	$63.85	$63.90
7 purchase totals =	$826.81		$899.6650	$899.66	$899.65	$899.50