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	$90.83	9.484%	$99.4443	$99.44	$99.45	$99.40
Purchase #2	$18.56	7.770%	$20.0021	$20.00	$20.00	$20.00
Purchase #3	$226.89	6.863%	$242.4615	$242.46	$242.45	$242.50
Purchase #4	$174.71	12.270%	$196.1469	$196.15	$196.15	$196.10
Purchase #5	$8.40	12.533%	$9.4528	$9.45	$9.45	$9.50
Purchase #6	$63.27	7.798%	$68.2038	$68.20	$68.20	$68.20
Purchase #7	$52.44	3.672%	$54.3656	$54.37	$54.35	$54.40
7 purchase totals =	$635.10		$690.0770	$690.07	$690.05	$690.10