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	$24.64	3.743%	$25.5623	$25.56	$25.55	$25.60
Purchase #2	$164.29	13.523%	$186.5069	$186.51	$186.50	$186.50
Purchase #3	$139.52	4.354%	$145.5947	$145.59	$145.60	$145.60
Purchase #4	$117.65	6.827%	$125.682	$125.68	$125.70	$125.70
Purchase #5	$89.56	12.580%	$100.8266	$100.83	$100.85	$100.80
Purchase #6	$215.33	10.782%	$238.5469	$238.55	$238.55	$238.50
Purchase #7	$19.72	8.374%	$21.3714	$21.37	$21.35	$21.40
7 purchase totals =	$770.71		$844.0908	$844.09	$844.10	$844.10