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	$239.90	12.452%	$269.7723	$269.77	$269.75	$269.80
Purchase #2	$40.47	12.268%	$45.4349	$45.43	$45.45	$45.40
Purchase #3	$39.57	7.667%	$42.6038	$42.60	$42.60	$42.60
Purchase #4	$56.50	10.362%	$62.3545	$62.35	$62.35	$62.40
Purchase #5	$177.71	12.736%	$200.3431	$200.34	$200.35	$200.30
Purchase #6	$157.97	5.108%	$166.0391	$166.04	$166.05	$166.00
Purchase #7	$9.69	11.729%	$10.8265	$10.83	$10.85	$10.80
7 purchase totals =	$721.81		$797.3742	$797.36	$797.40	$797.30