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	$41.40	3.528%	$42.8606	$42.86	$42.85	$42.90
Purchase #2	$107.86	6.102%	$114.4416	$114.44	$114.45	$114.40
Purchase #3	$138.86	3.365%	$143.5326	$143.53	$143.55	$143.50
Purchase #4	$86.37	5.492%	$91.1134	$91.11	$91.10	$91.10
Purchase #5	$6.96	13.560%	$7.9038	$7.90	$7.90	$7.90
Purchase #6	$66.74	10.685%	$73.8712	$73.87	$73.85	$73.90
Purchase #7	$132.30	5.422%	$139.4733	$139.47	$139.45	$139.50
7 purchase totals =	$580.49		$613.1965	$613.18	$613.15	$613.20