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	$109.99	12.371%	$123.5969	$123.60	$123.60	$123.60
Purchase #2	$118.63	7.562%	$127.6008	$127.60	$127.60	$127.60
Purchase #3	$154.44	8.234%	$167.1566	$167.16	$167.15	$167.20
Purchase #4	$172.52	11.575%	$192.4892	$192.49	$192.50	$192.50
Purchase #5	$136.60	4.537%	$142.7975	$142.80	$142.80	$142.80
Purchase #6	$51.89	10.794%	$57.491	$57.49	$57.50	$57.50
Purchase #7	$106.64	3.422%	$110.2892	$110.29	$110.30	$110.30
7 purchase totals =	$850.71		$921.4212	$921.43	$921.45	$921.50