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	$114.85	7.125%	$123.0331	$123.03	$123.05	$123.00
Purchase #2	$171.42	11.843%	$191.7213	$191.72	$191.70	$191.70
Purchase #3	$102.73	5.722%	$108.6082	$108.61	$108.60	$108.60
Purchase #4	$113.73	7.670%	$122.4531	$122.45	$122.45	$122.50
Purchase #5	$65.73	9.861%	$72.2116	$72.21	$72.20	$72.20
Purchase #6	$135.89	13.672%	$154.4689	$154.47	$154.45	$154.50
Purchase #7	$132.52	8.127%	$143.2899	$143.29	$143.30	$143.30
7 purchase totals =	$836.87		$915.7861	$915.78	$915.75	$915.80