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	$70.43	8.162%	$76.1785	$76.18	$76.20	$76.20
Purchase #2	$231.34	3.128%	$238.5763	$238.58	$238.60	$238.60
Purchase #3	$112.72	4.230%	$117.4881	$117.49	$117.50	$117.50
Purchase #4	$163.86	13.340%	$185.7189	$185.72	$185.70	$185.70
Purchase #5	$98.44	12.763%	$111.0039	$111.00	$111.00	$111.00
Purchase #6	$76.38	13.506%	$86.6959	$86.70	$86.70	$86.70
Purchase #7	$137.75	13.536%	$156.3958	$156.40	$156.40	$156.40
7 purchase totals =	$890.92		$972.0574	$972.07	$972.10	$972.10