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	$54.28	9.832%	$59.6168	$59.62	$59.60	$59.60
Purchase #2	$183.94	8.700%	$199.9428	$199.94	$199.95	$199.90
Purchase #3	$153.77	12.664%	$173.2434	$173.24	$173.25	$173.20
Purchase #4	$161.44	12.694%	$181.9332	$181.93	$181.95	$181.90
Purchase #5	$30.76	9.540%	$33.6945	$33.69	$33.70	$33.70
Purchase #6	$46.35	13.509%	$52.6114	$52.61	$52.60	$52.60
Purchase #7	$235.52	12.496%	$264.9506	$264.95	$264.95	$265.00
7 purchase totals =	$866.06		$965.9927	$965.98	$966.00	$965.90