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	$120.35	6.840%	$128.5819	$128.58	$128.60	$128.60
Purchase #2	$58.62	6.576%	$62.4749	$62.47	$62.45	$62.50
Purchase #3	$95.37	8.550%	$103.5241	$103.52	$103.50	$103.50
Purchase #4	$56.93	8.748%	$61.9102	$61.91	$61.90	$61.90
Purchase #5	$137.60	9.688%	$150.9307	$150.93	$150.95	$150.90
Purchase #6	$177.39	9.471%	$194.1906	$194.19	$194.20	$194.20
Purchase #7	$19.62	10.695%	$21.7184	$21.72	$21.70	$21.70
7 purchase totals =	$665.88		$723.3308	$723.32	$723.30	$723.30