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	$71.25	11.863%	$79.7024	$79.70	$79.70	$79.70
Purchase #2	$113.83	3.571%	$117.8949	$117.89	$117.90	$117.90
Purchase #3	$171.76	10.687%	$190.116	$190.12	$190.10	$190.10
Purchase #4	$93.46	11.334%	$104.0528	$104.05	$104.05	$104.10
Purchase #5	$216.82	11.828%	$242.4655	$242.47	$242.45	$242.50
Purchase #6	$93.99	12.513%	$105.751	$105.75	$105.75	$105.80
Purchase #7	$124.61	12.837%	$140.6062	$140.61	$140.60	$140.60
7 purchase totals =	$885.72		$980.5888	$980.59	$980.55	$980.70