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	$107.63	9.194%	$117.5255	$117.53	$117.55	$117.50
Purchase #2	$217.70	9.605%	$238.6101	$238.61	$238.60	$238.60
Purchase #3	$132.45	5.392%	$139.5917	$139.59	$139.60	$139.60
Purchase #4	$154.54	7.241%	$165.7302	$165.73	$165.75	$165.70
Purchase #5	$28.61	11.406%	$31.8733	$31.87	$31.85	$31.90
Purchase #6	$42.97	12.623%	$48.3941	$48.39	$48.40	$48.40
Purchase #7	$109.55	13.565%	$124.4105	$124.41	$124.40	$124.40
7 purchase totals =	$793.45		$866.1354	$866.13	$866.15	$866.10