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	$90.35	13.103%	$102.1886	$102.19	$102.20	$102.20
Purchase #2	$85.63	13.844%	$97.4846	$97.48	$97.50	$97.50
Purchase #3	$143.59	11.678%	$160.3584	$160.36	$160.35	$160.40
Purchase #4	$137.96	3.820%	$143.2301	$143.23	$143.25	$143.20
Purchase #5	$74.97	5.162%	$78.84	$78.84	$78.85	$78.80
Purchase #6	$128.60	8.583%	$139.6377	$139.64	$139.65	$139.60
Purchase #7	$195.70	13.576%	$222.2682	$222.27	$222.25	$222.30
7 purchase totals =	$856.80		$944.0076	$944.01	$944.05	$944.00