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	$16.25	12.359%	$18.2583	$18.26	$18.25	$18.30
Purchase #2	$214.43	4.827%	$224.7805	$224.78	$224.80	$224.80
Purchase #3	$71.42	7.436%	$76.7308	$76.73	$76.75	$76.70
Purchase #4	$80.43	13.761%	$91.498	$91.50	$91.50	$91.50
Purchase #5	$38.85	13.706%	$44.1748	$44.17	$44.15	$44.20
Purchase #6	$39.38	7.725%	$42.4221	$42.42	$42.40	$42.40
Purchase #7	$200.83	4.765%	$210.3995	$210.40	$210.40	$210.40
7 purchase totals =	$661.59		$708.2640	$708.26	$708.25	$708.30