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	$39.58	8.103%	$42.7872	$42.79	$42.80	$42.80
Purchase #2	$117.58	9.234%	$128.4373	$128.44	$128.45	$128.40
Purchase #3	$228.64	12.613%	$257.4784	$257.48	$257.50	$257.50
Purchase #4	$179.99	9.130%	$196.4231	$196.42	$196.40	$196.40
Purchase #5	$142.89	10.596%	$158.0306	$158.03	$158.05	$158.00
Purchase #6	$85.63	5.599%	$90.4244	$90.42	$90.40	$90.40
Purchase #7	$140.66	12.623%	$158.4155	$158.42	$158.40	$158.40
7 purchase totals =	$934.97		$1,031.9965	$1,032.00	$1,032.00	$1,031.90