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	$25.68	12.400%	$28.8643	$28.86	$28.85	$28.90
Purchase #2	$55.80	10.145%	$61.4609	$61.46	$61.45	$61.50
Purchase #3	$72.99	13.286%	$82.6875	$82.69	$82.70	$82.70
Purchase #4	$114.78	10.602%	$126.949	$126.95	$126.95	$126.90
Purchase #5	$38.56	11.174%	$42.8687	$42.87	$42.85	$42.90
Purchase #6	$183.51	6.623%	$195.6639	$195.66	$195.65	$195.70
Purchase #7	$56.81	6.427%	$60.4612	$60.46	$60.45	$60.50
7 purchase totals =	$548.13		$598.9555	$598.95	$598.90	$599.10