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	$112.79	9.309%	$123.2896	$123.29	$123.30	$123.30
Purchase #2	$6.51	9.537%	$7.1309	$7.13	$7.15	$7.10
Purchase #3	$230.54	3.753%	$239.1922	$239.19	$239.20	$239.20
Purchase #4	$18.32	13.756%	$20.8401	$20.84	$20.85	$20.80
Purchase #5	$21.80	10.671%	$24.1263	$24.13	$24.15	$24.10
Purchase #6	$26.98	10.495%	$29.8116	$29.81	$29.80	$29.80
Purchase #7	$113.56	12.251%	$127.4722	$127.47	$127.45	$127.50
7 purchase totals =	$530.50		$571.8629	$571.86	$571.90	$571.80