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	$18.57	4.613%	$19.4266	$19.43	$19.45	$19.40
Purchase #2	$158.53	12.517%	$178.3732	$178.37	$178.35	$178.40
Purchase #3	$141.37	11.790%	$158.0375	$158.04	$158.05	$158.00
Purchase #4	$96.87	6.822%	$103.4785	$103.48	$103.50	$103.50
Purchase #5	$242.81	5.214%	$255.4701	$255.47	$255.45	$255.50
Purchase #6	$228.89	13.538%	$259.8771	$259.88	$259.90	$259.90
Purchase #7	$176.40	7.542%	$189.7041	$189.70	$189.70	$189.70
7 purchase totals =	$1,063.44		$1,164.3671	$1,164.37	$1,164.40	$1,164.40