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	$25.35	12.815%	$28.5986	$28.60	$28.60	$28.60
Purchase #2	$85.36	5.660%	$90.1914	$90.19	$90.20	$90.20
Purchase #3	$66.95	7.631%	$72.059	$72.06	$72.05	$72.10
Purchase #4	$17.77	11.532%	$19.8192	$19.82	$19.80	$19.80
Purchase #5	$214.38	12.646%	$241.4905	$241.49	$241.50	$241.50
Purchase #6	$241.99	8.606%	$262.8157	$262.82	$262.80	$262.80
Purchase #7	$173.25	8.197%	$187.4513	$187.45	$187.45	$187.50
7 purchase totals =	$825.05		$902.4257	$902.43	$902.40	$902.50