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	$63.68	6.178%	$67.6142	$67.61	$67.60	$67.60
Purchase #2	$63.41	4.655%	$66.3617	$66.36	$66.35	$66.40
Purchase #3	$124.37	11.440%	$138.5979	$138.60	$138.60	$138.60
Purchase #4	$170.71	3.197%	$176.1676	$176.17	$176.15	$176.20
Purchase #5	$92.53	13.125%	$104.6746	$104.67	$104.65	$104.70
Purchase #6	$12.37	12.373%	$13.9005	$13.90	$13.90	$13.90
Purchase #7	$92.93	7.698%	$100.0838	$100.08	$100.10	$100.10
7 purchase totals =	$620.00		$667.4003	$667.39	$667.35	$667.50