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	$121.28	5.204%	$127.5914	$127.59	$127.60	$127.60
Purchase #2	$192.50	3.545%	$199.3241	$199.32	$199.30	$199.30
Purchase #3	$12.80	8.400%	$13.8752	$13.88	$13.90	$13.90
Purchase #4	$109.92	9.103%	$119.926	$119.93	$119.95	$119.90
Purchase #5	$82.54	7.622%	$88.8312	$88.83	$88.85	$88.80
Purchase #6	$165.82	7.475%	$178.215	$178.22	$178.20	$178.20
Purchase #7	$25.39	12.576%	$28.583	$28.58	$28.60	$28.60
7 purchase totals =	$710.25		$756.3459	$756.35	$756.40	$756.30