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	$241.59	12.204%	$271.0736	$271.07	$271.05	$271.10
Purchase #2	$37.60	13.249%	$42.5816	$42.58	$42.60	$42.60
Purchase #3	$125.35	4.620%	$131.1412	$131.14	$131.15	$131.10
Purchase #4	$201.65	3.723%	$209.1574	$209.16	$209.15	$209.20
Purchase #5	$131.58	4.182%	$137.0827	$137.08	$137.10	$137.10
Purchase #6	$28.68	9.477%	$31.398	$31.40	$31.40	$31.40
Purchase #7	$13.45	4.749%	$14.0887	$14.09	$14.10	$14.10
7 purchase totals =	$779.90		$836.5232	$836.52	$836.55	$836.60