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	$127.48	9.563%	$139.6709	$139.67	$139.65	$139.70
Purchase #2	$30.78	7.260%	$33.0146	$33.01	$33.00	$33.00
Purchase #3	$108.26	10.475%	$119.6002	$119.60	$119.60	$119.60
Purchase #4	$21.32	3.539%	$22.0745	$22.07	$22.05	$22.10
Purchase #5	$90.39	10.798%	$100.1503	$100.15	$100.15	$100.20
Purchase #6	$60.29	3.475%	$62.3851	$62.39	$62.40	$62.40
Purchase #7	$130.42	10.533%	$144.1571	$144.16	$144.15	$144.20
7 purchase totals =	$568.94		$621.0527	$621.05	$621.00	$621.20