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	$128.68	12.256%	$144.451	$144.45	$144.45	$144.50
Purchase #2	$109.61	7.244%	$117.5501	$117.55	$117.55	$117.60
Purchase #3	$144.47	11.465%	$161.0335	$161.03	$161.05	$161.00
Purchase #4	$198.88	7.861%	$214.514	$214.51	$214.50	$214.50
Purchase #5	$246.42	4.726%	$258.0658	$258.07	$258.05	$258.10
Purchase #6	$160.40	7.158%	$171.8814	$171.88	$171.90	$171.90
Purchase #7	$84.51	5.433%	$89.1014	$89.10	$89.10	$89.10
7 purchase totals =	$1,072.97		$1,156.5972	$1,156.59	$1,156.60	$1,156.70