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	$87.31	3.681%	$90.5239	$90.52	$90.50	$90.50
Purchase #2	$181.29	11.735%	$202.5644	$202.56	$202.55	$202.60
Purchase #3	$197.83	12.141%	$221.8485	$221.85	$221.85	$221.80
Purchase #4	$108.25	7.319%	$116.1728	$116.17	$116.15	$116.20
Purchase #5	$15.77	13.522%	$17.9024	$17.90	$17.90	$17.90
Purchase #6	$138.32	9.233%	$151.0911	$151.09	$151.10	$151.10
Purchase #7	$154.47	8.622%	$167.7884	$167.79	$167.80	$167.80
7 purchase totals =	$883.24		$967.8915	$967.88	$967.85	$967.90