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	$212.84	12.761%	$240.0005	$240.00	$240.00	$240.00
Purchase #2	$112.61	13.330%	$127.6209	$127.62	$127.60	$127.60
Purchase #3	$247.63	3.606%	$256.5595	$256.56	$256.55	$256.60
Purchase #4	$222.89	7.684%	$240.0169	$240.02	$240.00	$240.00
Purchase #5	$169.69	7.588%	$182.5661	$182.57	$182.55	$182.60
Purchase #6	$133.45	3.385%	$137.9673	$137.97	$137.95	$138.00
Purchase #7	$47.32	11.532%	$52.7769	$52.78	$52.80	$52.80
7 purchase totals =	$1,146.43		$1,237.5081	$1,237.52	$1,237.45	$1,237.60