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	$31.46	9.664%	$34.5003	$34.50	$34.50	$34.50
Purchase #2	$39.45	7.413%	$42.3744	$42.37	$42.35	$42.40
Purchase #3	$216.83	13.177%	$245.4017	$245.40	$245.40	$245.40
Purchase #4	$169.75	5.799%	$179.5938	$179.59	$179.60	$179.60
Purchase #5	$39.82	9.379%	$43.5547	$43.55	$43.55	$43.60
Purchase #6	$126.59	10.623%	$140.0377	$140.04	$140.05	$140.00
Purchase #7	$163.97	11.382%	$182.6331	$182.63	$182.65	$182.60
7 purchase totals =	$787.87		$868.0957	$868.08	$868.10	$868.10