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	$15.77	6.509%	$16.7965	$16.80	$16.80	$16.80
Purchase #2	$45.73	4.702%	$47.8802	$47.88	$47.90	$47.90
Purchase #3	$100.84	13.660%	$114.6147	$114.61	$114.60	$114.60
Purchase #4	$80.29	11.390%	$89.435	$89.44	$89.45	$89.40
Purchase #5	$217.64	7.712%	$234.4244	$234.42	$234.40	$234.40
Purchase #6	$232.60	4.539%	$243.1577	$243.16	$243.15	$243.20
Purchase #7	$136.66	5.275%	$143.8688	$143.87	$143.85	$143.90
7 purchase totals =	$829.53		$890.1773	$890.18	$890.15	$890.20