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	$40.28	11.290%	$44.8276	$44.83	$44.85	$44.80
Purchase #2	$137.36	13.296%	$155.6234	$155.62	$155.60	$155.60
Purchase #3	$16.82	12.175%	$18.8678	$18.87	$18.85	$18.90
Purchase #4	$16.83	4.233%	$17.5424	$17.54	$17.55	$17.50
Purchase #5	$102.72	3.120%	$105.9249	$105.92	$105.90	$105.90
Purchase #6	$192.46	6.635%	$205.2297	$205.23	$205.25	$205.20
Purchase #7	$88.85	10.440%	$98.1259	$98.13	$98.15	$98.10
7 purchase totals =	$595.32		$646.1417	$646.14	$646.15	$646.00