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	$85.79	5.451%	$90.4664	$90.47	$90.45	$90.50
Purchase #2	$158.61	12.464%	$178.3792	$178.38	$178.40	$178.40
Purchase #3	$14.75	5.680%	$15.5878	$15.59	$15.60	$15.60
Purchase #4	$22.29	11.159%	$24.7773	$24.78	$24.80	$24.80
Purchase #5	$131.28	4.364%	$137.0091	$137.01	$137.00	$137.00
Purchase #6	$133.76	5.673%	$141.3482	$141.35	$141.35	$141.30
Purchase #7	$178.94	4.650%	$187.2607	$187.26	$187.25	$187.30
7 purchase totals =	$725.42		$774.8287	$774.84	$774.85	$774.90