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	$46.45	11.635%	$51.8545	$51.85	$51.85	$51.90
Purchase #2	$66.40	7.763%	$71.5546	$71.55	$71.55	$71.60
Purchase #3	$49.83	8.658%	$54.1443	$54.14	$54.15	$54.10
Purchase #4	$34.73	11.196%	$38.6184	$38.62	$38.60	$38.60
Purchase #5	$117.83	11.819%	$131.7563	$131.76	$131.75	$131.80
Purchase #6	$176.69	3.780%	$183.3689	$183.37	$183.35	$183.40
Purchase #7	$41.90	4.551%	$43.8069	$43.81	$43.80	$43.80
7 purchase totals =	$533.83		$575.1039	$575.10	$575.05	$575.20