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	$16.86	3.630%	$17.472	$17.47	$17.45	$17.50
Purchase #2	$137.81	4.665%	$144.2388	$144.24	$144.25	$144.20
Purchase #3	$90.47	6.718%	$96.5478	$96.55	$96.55	$96.50
Purchase #4	$210.33	8.571%	$228.3574	$228.36	$228.35	$228.40
Purchase #5	$119.46	6.527%	$127.2572	$127.26	$127.25	$127.30
Purchase #6	$75.86	3.590%	$78.5834	$78.58	$78.60	$78.60
Purchase #7	$69.96	10.140%	$77.0539	$77.05	$77.05	$77.10
7 purchase totals =	$720.75		$769.5105	$769.51	$769.50	$769.60