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	$84.66	5.205%	$89.0666	$89.07	$89.05	$89.10
Purchase #2	$13.55	5.821%	$14.3387	$14.34	$14.35	$14.30
Purchase #3	$161.51	6.757%	$172.4232	$172.42	$172.40	$172.40
Purchase #4	$121.69	8.611%	$132.1687	$132.17	$132.15	$132.20
Purchase #5	$37.88	6.283%	$40.26	$40.26	$40.25	$40.30
Purchase #6	$40.68	4.248%	$42.4081	$42.41	$42.40	$42.40
Purchase #7	$90.83	6.594%	$96.8193	$96.82	$96.80	$96.80
7 purchase totals =	$550.80		$587.4846	$587.49	$587.40	$587.50