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	$168.62	9.774%	$185.1009	$185.10	$185.10	$185.10
Purchase #2	$36.59	7.314%	$39.2662	$39.27	$39.25	$39.30
Purchase #3	$234.72	10.329%	$258.9642	$258.96	$258.95	$259.00
Purchase #4	$162.96	9.720%	$178.7997	$178.80	$178.80	$178.80
Purchase #5	$20.81	3.758%	$21.592	$21.59	$21.60	$21.60
Purchase #6	$45.43	13.550%	$51.5858	$51.59	$51.60	$51.60
Purchase #7	$236.25	11.273%	$262.8825	$262.88	$262.90	$262.90
7 purchase totals =	$905.38		$998.1913	$998.19	$998.20	$998.30