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	$101.94	12.149%	$114.3247	$114.32	$114.30	$114.30
Purchase #2	$97.53	6.127%	$103.5057	$103.51	$103.50	$103.50
Purchase #3	$146.84	13.421%	$166.5474	$166.55	$166.55	$166.50
Purchase #4	$182.37	12.737%	$205.5985	$205.60	$205.60	$205.60
Purchase #5	$92.47	12.300%	$103.8438	$103.84	$103.85	$103.80
Purchase #6	$47.81	8.281%	$51.7691	$51.77	$51.75	$51.80
Purchase #7	$137.39	4.463%	$143.5217	$143.52	$143.50	$143.50
7 purchase totals =	$806.35		$889.1109	$889.11	$889.05	$889.00