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	$154.83	6.589%	$165.0317	$165.03	$165.05	$165.00
Purchase #2	$56.68	8.381%	$61.4304	$61.43	$61.45	$61.40
Purchase #3	$166.57	8.342%	$180.4653	$180.47	$180.45	$180.50
Purchase #4	$150.42	10.828%	$166.7075	$166.71	$166.70	$166.70
Purchase #5	$141.85	5.765%	$150.0277	$150.03	$150.05	$150.00
Purchase #6	$84.88	12.466%	$95.4611	$95.46	$95.45	$95.50
Purchase #7	$76.48	8.844%	$83.2439	$83.24	$83.25	$83.20
7 purchase totals =	$831.71		$902.3676	$902.37	$902.40	$902.30