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	$28.39	13.442%	$32.2062	$32.21	$32.20	$32.20
Purchase #2	$122.61	9.826%	$134.6577	$134.66	$134.65	$134.70
Purchase #3	$141.72	11.733%	$158.348	$158.35	$158.35	$158.30
Purchase #4	$45.36	9.627%	$49.7268	$49.73	$49.75	$49.70
Purchase #5	$119.61	7.278%	$128.3152	$128.32	$128.30	$128.30
Purchase #6	$77.43	10.113%	$85.2605	$85.26	$85.25	$85.30
Purchase #7	$233.73	9.313%	$255.4973	$255.50	$255.50	$255.50
7 purchase totals =	$768.85		$844.0117	$844.03	$844.00	$844.00