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	$166.42	7.714%	$179.2576	$179.26	$179.25	$179.30
Purchase #2	$40.46	6.410%	$43.0535	$43.05	$43.05	$43.10
Purchase #3	$68.48	8.117%	$74.0385	$74.04	$74.05	$74.00
Purchase #4	$132.93	9.464%	$145.5105	$145.51	$145.50	$145.50
Purchase #5	$77.68	11.309%	$86.4648	$86.46	$86.45	$86.50
Purchase #6	$12.33	8.105%	$13.3293	$13.33	$13.35	$13.30
Purchase #7	$114.51	7.572%	$123.1807	$123.18	$123.20	$123.20
7 purchase totals =	$612.81		$664.8349	$664.83	$664.85	$664.90