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	$24.84	9.794%	$27.2728	$27.27	$27.25	$27.30
Purchase #2	$142.32	10.575%	$157.3703	$157.37	$157.35	$157.40
Purchase #3	$75.38	4.552%	$78.8113	$78.81	$78.80	$78.80
Purchase #4	$145.58	9.139%	$158.8846	$158.88	$158.90	$158.90
Purchase #5	$36.39	6.255%	$38.6662	$38.67	$38.65	$38.70
Purchase #6	$55.69	12.683%	$62.7532	$62.75	$62.75	$62.80
Purchase #7	$116.75	8.226%	$126.3539	$126.35	$126.35	$126.40
7 purchase totals =	$596.95		$650.1123	$650.10	$650.05	$650.30