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	$126.69	8.467%	$137.4168	$137.42	$137.40	$137.40
Purchase #2	$64.78	12.549%	$72.9092	$72.91	$72.90	$72.90
Purchase #3	$203.39	11.743%	$227.2741	$227.27	$227.25	$227.30
Purchase #4	$17.39	6.568%	$18.5322	$18.53	$18.55	$18.50
Purchase #5	$163.68	8.347%	$177.3424	$177.34	$177.35	$177.30
Purchase #6	$131.93	7.196%	$141.4237	$141.42	$141.40	$141.40
Purchase #7	$18.67	12.533%	$21.0099	$21.01	$21.00	$21.00
7 purchase totals =	$726.53		$795.9083	$795.90	$795.85	$795.80