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	$215.67	5.823%	$228.2285	$228.23	$228.25	$228.20
Purchase #2	$181.61	4.844%	$190.4072	$190.41	$190.40	$190.40
Purchase #3	$86.39	5.161%	$90.8486	$90.85	$90.85	$90.80
Purchase #4	$29.81	12.701%	$33.5962	$33.60	$33.60	$33.60
Purchase #5	$95.86	4.748%	$100.4114	$100.41	$100.40	$100.40
Purchase #6	$137.93	11.836%	$154.2554	$154.26	$154.25	$154.30
Purchase #7	$102.70	9.106%	$112.0519	$112.05	$112.05	$112.10
7 purchase totals =	$849.97		$909.7992	$909.81	$909.80	$909.80