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	$37.51	6.735%	$40.0363	$40.04	$40.05	$40.00
Purchase #2	$103.31	4.105%	$107.5509	$107.55	$107.55	$107.60
Purchase #3	$208.29	7.635%	$224.1929	$224.19	$224.20	$224.20
Purchase #4	$21.61	13.427%	$24.5116	$24.51	$24.50	$24.50
Purchase #5	$55.37	10.317%	$61.0825	$61.08	$61.10	$61.10
Purchase #6	$48.58	6.256%	$51.6192	$51.62	$51.60	$51.60
Purchase #7	$112.84	4.803%	$118.2597	$118.26	$118.25	$118.30
7 purchase totals =	$587.51		$627.2531	$627.25	$627.25	$627.30