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	$227.85	11.240%	$253.4603	$253.46	$253.45	$253.50
Purchase #2	$14.57	8.711%	$15.8392	$15.84	$15.85	$15.80
Purchase #3	$29.45	10.725%	$32.6085	$32.61	$32.60	$32.60
Purchase #4	$123.84	12.687%	$139.5516	$139.55	$139.55	$139.60
Purchase #5	$228.68	12.537%	$257.3496	$257.35	$257.35	$257.30
Purchase #6	$39.84	6.540%	$42.4455	$42.45	$42.45	$42.40
Purchase #7	$46.32	11.231%	$51.5222	$51.52	$51.50	$51.50
7 purchase totals =	$710.55		$792.7769	$792.78	$792.75	$792.70