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	$19.67	12.693%	$22.1667	$22.17	$22.15	$22.20
Purchase #2	$201.25	8.282%	$217.9175	$217.92	$217.90	$217.90
Purchase #3	$142.82	7.149%	$153.0302	$153.03	$153.05	$153.00
Purchase #4	$125.89	12.733%	$141.9196	$141.92	$141.90	$141.90
Purchase #5	$93.96	4.103%	$97.8152	$97.82	$97.80	$97.80
Purchase #6	$77.70	10.533%	$85.8841	$85.88	$85.90	$85.90
Purchase #7	$104.52	6.450%	$111.2615	$111.26	$111.25	$111.30
7 purchase totals =	$765.81		$829.9948	$830.00	$829.95	$830.00