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	$20.55	9.361%	$22.4737	$22.47	$22.45	$22.50
Purchase #2	$93.90	7.134%	$100.5988	$100.60	$100.60	$100.60
Purchase #3	$92.81	12.506%	$104.4168	$104.42	$104.40	$104.40
Purchase #4	$41.27	10.635%	$45.6591	$45.66	$45.65	$45.70
Purchase #5	$102.59	5.681%	$108.4181	$108.42	$108.40	$108.40
Purchase #6	$34.54	12.332%	$38.7995	$38.80	$38.80	$38.80
Purchase #7	$179.61	3.671%	$186.2035	$186.20	$186.20	$186.20
7 purchase totals =	$565.27		$606.5695	$606.57	$606.50	$606.60