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	$39.79	6.837%	$42.5104	$42.51	$42.50	$42.50
Purchase #2	$105.34	5.789%	$111.4381	$111.44	$111.45	$111.40
Purchase #3	$225.39	6.201%	$239.3664	$239.37	$239.35	$239.40
Purchase #4	$123.44	13.493%	$140.0958	$140.10	$140.10	$140.10
Purchase #5	$90.70	13.315%	$102.7767	$102.78	$102.80	$102.80
Purchase #6	$126.35	8.539%	$137.139	$137.14	$137.15	$137.10
Purchase #7	$207.44	11.214%	$230.7023	$230.70	$230.70	$230.70
7 purchase totals =	$918.45		$1,004.0287	$1,004.04	$1,004.05	$1,004.00