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	$111.93	11.554%	$124.8624	$124.86	$124.85	$124.90
Purchase #2	$140.98	12.246%	$158.2444	$158.24	$158.25	$158.20
Purchase #3	$138.62	8.262%	$150.0728	$150.07	$150.05	$150.10
Purchase #4	$98.68	3.492%	$102.1259	$102.13	$102.15	$102.10
Purchase #5	$192.58	6.715%	$205.5117	$205.51	$205.50	$205.50
Purchase #6	$117.72	13.384%	$133.4756	$133.48	$133.50	$133.50
Purchase #7	$208.96	7.816%	$225.2923	$225.29	$225.30	$225.30
7 purchase totals =	$1,009.47		$1,099.5851	$1,099.58	$1,099.60	$1,099.60