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	$105.26	8.196%	$113.8871	$113.89	$113.90	$113.90
Purchase #2	$99.83	12.139%	$111.9484	$111.95	$111.95	$111.90
Purchase #3	$34.83	12.755%	$39.2726	$39.27	$39.25	$39.30
Purchase #4	$83.42	7.436%	$89.6231	$89.62	$89.60	$89.60
Purchase #5	$176.67	12.252%	$198.3156	$198.32	$198.30	$198.30
Purchase #6	$239.94	11.208%	$266.8325	$266.83	$266.85	$266.80
Purchase #7	$152.98	13.362%	$173.4212	$173.42	$173.40	$173.40
7 purchase totals =	$892.93		$993.3005	$993.30	$993.25	$993.20