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	$230.49	10.795%	$255.3714	$255.37	$255.35	$255.40
Purchase #2	$74.70	9.267%	$81.6224	$81.62	$81.60	$81.60
Purchase #3	$163.75	4.344%	$170.8633	$170.86	$170.85	$170.90
Purchase #4	$114.39	4.631%	$119.6874	$119.69	$119.70	$119.70
Purchase #5	$79.46	12.608%	$89.4783	$89.48	$89.50	$89.50
Purchase #6	$34.51	11.750%	$38.5649	$38.56	$38.55	$38.60
Purchase #7	$172.77	8.177%	$186.8974	$186.90	$186.90	$186.90
7 purchase totals =	$870.07		$942.4851	$942.48	$942.45	$942.60