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	$34.94	11.197%	$38.8522	$38.85	$38.85	$38.90
Purchase #2	$139.47	4.746%	$146.0892	$146.09	$146.10	$146.10
Purchase #3	$221.92	6.135%	$235.5348	$235.53	$235.55	$235.50
Purchase #4	$38.73	9.492%	$42.4063	$42.41	$42.40	$42.40
Purchase #5	$116.54	6.186%	$123.7492	$123.75	$123.75	$123.70
Purchase #6	$117.47	12.183%	$131.7814	$131.78	$131.80	$131.80
Purchase #7	$83.80	10.382%	$92.5001	$92.50	$92.50	$92.50
7 purchase totals =	$752.87		$810.9132	$810.91	$810.95	$810.90