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	$43.90	10.589%	$48.5486	$48.55	$48.55	$48.50
Purchase #2	$190.49	12.344%	$214.0041	$214.00	$214.00	$214.00
Purchase #3	$168.63	13.352%	$191.1455	$191.15	$191.15	$191.10
Purchase #4	$96.97	8.172%	$104.8944	$104.89	$104.90	$104.90
Purchase #5	$96.95	7.119%	$103.8519	$103.85	$103.85	$103.90
Purchase #6	$38.93	11.746%	$43.5027	$43.50	$43.50	$43.50
Purchase #7	$60.45	4.634%	$63.2513	$63.25	$63.25	$63.30
7 purchase totals =	$696.32		$769.1985	$769.19	$769.20	$769.20