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	$108.27	4.189%	$112.8054	$112.81	$112.80	$112.80
Purchase #2	$76.52	5.161%	$80.4692	$80.47	$80.45	$80.50
Purchase #3	$119.79	10.215%	$132.0265	$132.03	$132.05	$132.00
Purchase #4	$18.79	11.544%	$20.9591	$20.96	$20.95	$21.00
Purchase #5	$228.99	11.687%	$255.7521	$255.75	$255.75	$255.80
Purchase #6	$36.88	6.622%	$39.3222	$39.32	$39.30	$39.30
Purchase #7	$75.35	11.221%	$83.805	$83.81	$83.80	$83.80
7 purchase totals =	$664.59		$725.1395	$725.15	$725.10	$725.20