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	$237.78	5.597%	$251.0885	$251.09	$251.10	$251.10
Purchase #2	$144.63	12.229%	$162.3168	$162.32	$162.30	$162.30
Purchase #3	$151.48	4.636%	$158.5026	$158.50	$158.50	$158.50
Purchase #4	$146.70	5.184%	$154.3049	$154.30	$154.30	$154.30
Purchase #5	$143.78	10.111%	$158.3176	$158.32	$158.30	$158.30
Purchase #6	$5.85	3.665%	$6.0644	$6.06	$6.05	$6.10
Purchase #7	$88.96	7.290%	$95.4452	$95.45	$95.45	$95.40
7 purchase totals =	$919.18		$986.0400	$986.04	$986.00	$986.00