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	$107.47	8.530%	$116.6372	$116.64	$116.65	$116.60
Purchase #2	$17.37	4.606%	$18.1701	$18.17	$18.15	$18.20
Purchase #3	$132.78	12.196%	$148.9738	$148.97	$148.95	$149.00
Purchase #4	$141.84	6.340%	$150.8327	$150.83	$150.85	$150.80
Purchase #5	$64.55	9.108%	$70.4292	$70.43	$70.45	$70.40
Purchase #6	$99.25	4.688%	$103.9028	$103.90	$103.90	$103.90
Purchase #7	$237.67	12.319%	$266.9486	$266.95	$266.95	$266.90
7 purchase totals =	$800.93		$875.8944	$875.89	$875.90	$875.80