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	$14.57	12.749%	$16.4275	$16.43	$16.45	$16.40
Purchase #2	$99.34	6.303%	$105.6014	$105.60	$105.60	$105.60
Purchase #3	$189.54	5.457%	$199.8832	$199.88	$199.90	$199.90
Purchase #4	$72.90	8.156%	$78.8457	$78.85	$78.85	$78.80
Purchase #5	$151.42	3.713%	$157.0422	$157.04	$157.05	$157.00
Purchase #6	$81.98	10.323%	$90.4428	$90.44	$90.45	$90.40
Purchase #7	$17.74	11.484%	$19.7773	$19.78	$19.80	$19.80
7 purchase totals =	$627.49		$668.0201	$668.02	$668.10	$667.90