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	$112.84	13.309%	$127.8579	$127.86	$127.85	$127.90
Purchase #2	$207.94	9.456%	$227.6028	$227.60	$227.60	$227.60
Purchase #3	$212.60	8.789%	$231.2854	$231.29	$231.30	$231.30
Purchase #4	$190.69	13.500%	$216.4332	$216.43	$216.45	$216.40
Purchase #5	$179.60	9.854%	$197.2978	$197.30	$197.30	$197.30
Purchase #6	$241.56	11.390%	$269.0737	$269.07	$269.05	$269.10
Purchase #7	$137.39	10.557%	$151.8943	$151.89	$151.90	$151.90
7 purchase totals =	$1,282.62		$1,421.4451	$1,421.44	$1,421.45	$1,421.50