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	$94.51	10.431%	$104.3683	$104.37	$104.35	$104.40
Purchase #2	$43.41	9.415%	$47.4971	$47.50	$47.50	$47.50
Purchase #3	$18.96	13.423%	$21.505	$21.51	$21.50	$21.50
Purchase #4	$138.60	4.103%	$144.2868	$144.29	$144.30	$144.30
Purchase #5	$146.73	9.669%	$160.9173	$160.92	$160.90	$160.90
Purchase #6	$83.47	9.716%	$91.5799	$91.58	$91.60	$91.60
Purchase #7	$183.38	12.196%	$205.745	$205.75	$205.75	$205.70
7 purchase totals =	$709.06		$775.8994	$775.92	$775.90	$775.90