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	$35.72	9.361%	$39.0637	$39.06	$39.05	$39.10
Purchase #2	$153.93	12.774%	$173.593	$173.59	$173.60	$173.60
Purchase #3	$174.42	12.743%	$196.6463	$196.65	$196.65	$196.60
Purchase #4	$61.25	4.167%	$63.8023	$63.80	$63.80	$63.80
Purchase #5	$189.60	4.628%	$198.3747	$198.37	$198.35	$198.40
Purchase #6	$20.57	6.526%	$21.9124	$21.91	$21.90	$21.90
Purchase #7	$83.75	13.242%	$94.8402	$94.84	$94.85	$94.80
7 purchase totals =	$719.24		$788.2326	$788.22	$788.20	$788.20