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	$227.52	8.739%	$247.403	$247.40	$247.40	$247.40
Purchase #2	$144.53	4.535%	$151.0844	$151.08	$151.10	$151.10
Purchase #3	$214.55	12.105%	$240.5213	$240.52	$240.50	$240.50
Purchase #4	$28.54	3.439%	$29.5215	$29.52	$29.50	$29.50
Purchase #5	$24.94	10.334%	$27.5173	$27.52	$27.50	$27.50
Purchase #6	$123.62	3.452%	$127.8874	$127.89	$127.90	$127.90
Purchase #7	$102.95	11.330%	$114.6142	$114.61	$114.60	$114.60
7 purchase totals =	$866.65		$938.5491	$938.54	$938.50	$938.50