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	$132.35	9.630%	$145.0953	$145.10	$145.10	$145.10
Purchase #2	$244.86	7.195%	$262.4777	$262.48	$262.50	$262.50
Purchase #3	$141.70	11.634%	$158.1854	$158.19	$158.20	$158.20
Purchase #4	$38.88	9.560%	$42.5969	$42.60	$42.60	$42.60
Purchase #5	$249.56	12.343%	$280.3632	$280.36	$280.35	$280.40
Purchase #6	$205.66	3.182%	$212.2041	$212.20	$212.20	$212.20
Purchase #7	$129.29	6.359%	$137.5116	$137.51	$137.50	$137.50
7 purchase totals =	$1,142.30		$1,238.4342	$1,238.44	$1,238.45	$1,238.50