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	$39.53	7.618%	$42.5414	$42.54	$42.55	$42.50
Purchase #2	$212.41	11.496%	$236.8287	$236.83	$236.85	$236.80
Purchase #3	$142.81	11.660%	$159.4616	$159.46	$159.45	$159.50
Purchase #4	$143.46	6.140%	$152.2684	$152.27	$152.25	$152.30
Purchase #5	$64.44	10.233%	$71.0341	$71.03	$71.05	$71.00
Purchase #6	$154.28	13.806%	$175.5799	$175.58	$175.60	$175.60
Purchase #7	$234.86	11.438%	$261.7233	$261.72	$261.70	$261.70
7 purchase totals =	$991.79		$1,099.4374	$1,099.43	$1,099.45	$1,099.40