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	$206.30	12.174%	$231.415	$231.42	$231.40	$231.40
Purchase #2	$135.87	12.550%	$152.9217	$152.92	$152.90	$152.90
Purchase #3	$34.93	7.622%	$37.5924	$37.59	$37.60	$37.60
Purchase #4	$239.44	13.807%	$272.4995	$272.50	$272.50	$272.50
Purchase #5	$127.65	13.312%	$144.6428	$144.64	$144.65	$144.60
Purchase #6	$10.51	5.192%	$11.0557	$11.06	$11.05	$11.10
Purchase #7	$60.57	3.792%	$62.8668	$62.87	$62.85	$62.90
7 purchase totals =	$815.27		$912.9939	$913.00	$912.95	$913.00