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	$204.81	6.839%	$218.817	$218.82	$218.80	$218.80
Purchase #2	$132.46	8.275%	$143.4211	$143.42	$143.40	$143.40
Purchase #3	$134.52	6.377%	$143.0983	$143.10	$143.10	$143.10
Purchase #4	$139.29	11.785%	$155.7053	$155.71	$155.70	$155.70
Purchase #5	$34.68	11.287%	$38.5943	$38.59	$38.60	$38.60
Purchase #6	$97.82	13.482%	$111.0081	$111.01	$111.00	$111.00
Purchase #7	$97.35	3.505%	$100.7621	$100.76	$100.75	$100.80
7 purchase totals =	$840.93		$911.4062	$911.41	$911.35	$911.40