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	$213.47	6.238%	$226.7863	$226.79	$226.80	$226.80
Purchase #2	$52.65	7.735%	$56.7225	$56.72	$56.70	$56.70
Purchase #3	$48.43	5.364%	$51.0278	$51.03	$51.05	$51.00
Purchase #4	$138.41	12.864%	$156.2151	$156.22	$156.20	$156.20
Purchase #5	$242.70	9.393%	$265.4968	$265.50	$265.50	$265.50
Purchase #6	$109.90	12.465%	$123.599	$123.60	$123.60	$123.60
Purchase #7	$50.89	4.226%	$53.0406	$53.04	$53.05	$53.00
7 purchase totals =	$856.45		$932.8881	$932.90	$932.90	$932.80