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	$18.66	10.349%	$20.5911	$20.59	$20.60	$20.60
Purchase #2	$226.94	11.433%	$252.8861	$252.89	$252.90	$252.90
Purchase #3	$78.38	12.104%	$87.8671	$87.87	$87.85	$87.90
Purchase #4	$117.52	12.690%	$132.4333	$132.43	$132.45	$132.40
Purchase #5	$149.33	7.522%	$160.5626	$160.56	$160.55	$160.60
Purchase #6	$57.34	6.146%	$60.8641	$60.86	$60.85	$60.90
Purchase #7	$63.35	7.189%	$67.9042	$67.90	$67.90	$67.90
7 purchase totals =	$711.52		$783.1085	$783.10	$783.10	$783.20