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	$56.83	3.178%	$58.6361	$58.64	$58.65	$58.60
Purchase #2	$42.63	10.343%	$47.0392	$47.04	$47.05	$47.00
Purchase #3	$59.28	11.500%	$66.0972	$66.10	$66.10	$66.10
Purchase #4	$159.70	9.467%	$174.8188	$174.82	$174.80	$174.80
Purchase #5	$238.67	11.141%	$265.2602	$265.26	$265.25	$265.30
Purchase #6	$142.48	10.789%	$157.8522	$157.85	$157.85	$157.90
Purchase #7	$83.47	8.815%	$90.8279	$90.83	$90.85	$90.80
7 purchase totals =	$783.06		$860.5316	$860.54	$860.55	$860.50