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	$244.95	4.488%	$255.9434	$255.94	$255.95	$255.90
Purchase #2	$232.52	10.767%	$257.5554	$257.56	$257.55	$257.60
Purchase #3	$125.82	7.698%	$135.5056	$135.51	$135.50	$135.50
Purchase #4	$102.63	7.713%	$110.5459	$110.55	$110.55	$110.50
Purchase #5	$30.52	6.821%	$32.6018	$32.60	$32.60	$32.60
Purchase #6	$139.51	3.303%	$144.118	$144.12	$144.10	$144.10
Purchase #7	$40.50	3.204%	$41.7976	$41.80	$41.80	$41.80
7 purchase totals =	$916.45		$978.0677	$978.08	$978.05	$978.00