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	$43.34	12.125%	$48.595	$48.60	$48.60	$48.60
Purchase #2	$128.96	6.583%	$137.4494	$137.45	$137.45	$137.40
Purchase #3	$127.95	3.109%	$131.928	$131.93	$131.95	$131.90
Purchase #4	$45.41	8.587%	$49.3094	$49.31	$49.30	$49.30
Purchase #5	$175.82	6.507%	$187.2606	$187.26	$187.25	$187.30
Purchase #6	$105.48	11.319%	$117.4193	$117.42	$117.40	$117.40
Purchase #7	$7.50	12.303%	$8.4227	$8.42	$8.40	$8.40
7 purchase totals =	$634.46		$680.3844	$680.39	$680.35	$680.30