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	$93.79	11.254%	$104.3451	$104.35	$104.35	$104.30
Purchase #2	$244.46	5.724%	$258.4529	$258.45	$258.45	$258.50
Purchase #3	$129.59	12.629%	$145.9559	$145.96	$145.95	$146.00
Purchase #4	$160.58	4.500%	$167.8061	$167.81	$167.80	$167.80
Purchase #5	$90.40	10.711%	$100.0827	$100.08	$100.10	$100.10
Purchase #6	$210.27	13.490%	$238.6354	$238.64	$238.65	$238.60
Purchase #7	$236.47	9.753%	$259.5329	$259.53	$259.55	$259.50
7 purchase totals =	$1,165.56		$1,274.8110	$1,274.82	$1,274.85	$1,274.80