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	$107.81	6.175%	$114.4673	$114.47	$114.45	$114.50
Purchase #2	$158.88	6.385%	$169.0245	$169.02	$169.00	$169.00
Purchase #3	$41.51	10.139%	$45.7187	$45.72	$45.70	$45.70
Purchase #4	$94.55	4.278%	$98.5948	$98.59	$98.60	$98.60
Purchase #5	$114.52	4.603%	$119.7914	$119.79	$119.80	$119.80
Purchase #6	$18.40	13.571%	$20.8971	$20.90	$20.90	$20.90
Purchase #7	$44.83	5.421%	$47.2602	$47.26	$47.25	$47.30
7 purchase totals =	$580.50		$615.7540	$615.75	$615.70	$615.80