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	$73.44	13.488%	$83.3456	$83.35	$83.35	$83.30
Purchase #2	$69.44	7.763%	$74.8306	$74.83	$74.85	$74.80
Purchase #3	$121.57	4.108%	$126.5641	$126.56	$126.55	$126.60
Purchase #4	$6.42	6.713%	$6.851	$6.85	$6.85	$6.90
Purchase #5	$42.86	9.732%	$47.0311	$47.03	$47.05	$47.00
Purchase #6	$72.60	13.563%	$82.4467	$82.45	$82.45	$82.40
Purchase #7	$214.40	4.247%	$223.5056	$223.51	$223.50	$223.50
7 purchase totals =	$600.73		$644.5747	$644.58	$644.60	$644.50