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	$100.90	12.462%	$113.4742	$113.47	$113.45	$113.50
Purchase #2	$69.34	4.669%	$72.5775	$72.58	$72.60	$72.60
Purchase #3	$137.42	11.224%	$152.844	$152.84	$152.85	$152.80
Purchase #4	$139.26	8.604%	$151.2419	$151.24	$151.25	$151.20
Purchase #5	$248.96	12.314%	$279.6169	$279.62	$279.60	$279.60
Purchase #6	$84.29	13.373%	$95.5621	$95.56	$95.55	$95.60
Purchase #7	$130.51	9.187%	$142.5	$142.50	$142.50	$142.50
7 purchase totals =	$910.68		$1,007.8166	$1,007.81	$1,007.80	$1,007.80