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	$26.62	13.613%	$30.2438	$30.24	$30.25	$30.20
Purchase #2	$181.56	9.655%	$199.0896	$199.09	$199.10	$199.10
Purchase #3	$168.40	13.266%	$190.7399	$190.74	$190.75	$190.70
Purchase #4	$208.34	5.849%	$220.5258	$220.53	$220.55	$220.50
Purchase #5	$49.78	9.417%	$54.4678	$54.47	$54.45	$54.50
Purchase #6	$133.61	4.671%	$139.8509	$139.85	$139.85	$139.90
Purchase #7	$93.56	7.389%	$100.4731	$100.47	$100.45	$100.50
7 purchase totals =	$861.87		$935.3909	$935.39	$935.40	$935.40