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	$44.56	10.820%	$49.3814	$49.38	$49.40	$49.40
Purchase #2	$32.93	4.553%	$34.4293	$34.43	$34.45	$34.40
Purchase #3	$57.90	9.650%	$63.4874	$63.49	$63.50	$63.50
Purchase #4	$142.43	11.565%	$158.902	$158.90	$158.90	$158.90
Purchase #5	$166.82	12.567%	$187.7843	$187.78	$187.80	$187.80
Purchase #6	$14.82	3.309%	$15.3104	$15.31	$15.30	$15.30
Purchase #7	$187.47	9.498%	$205.2759	$205.28	$205.30	$205.30
7 purchase totals =	$646.93		$714.5707	$714.57	$714.65	$714.60