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	$53.76	6.762%	$57.3953	$57.40	$57.40	$57.40
Purchase #2	$91.50	8.524%	$99.2995	$99.30	$99.30	$99.30
Purchase #3	$70.78	8.208%	$76.5896	$76.59	$76.60	$76.60
Purchase #4	$157.57	10.755%	$174.5167	$174.52	$174.50	$174.50
Purchase #5	$12.94	13.818%	$14.728	$14.73	$14.75	$14.70
Purchase #6	$62.48	4.305%	$65.1698	$65.17	$65.15	$65.20
Purchase #7	$177.55	12.857%	$200.3776	$200.38	$200.40	$200.40
7 purchase totals =	$626.58		$688.0765	$688.09	$688.10	$688.10