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	$35.58	10.630%	$39.3622	$39.36	$39.35	$39.40
Purchase #2	$222.80	5.858%	$235.8516	$235.85	$235.85	$235.90
Purchase #3	$235.38	11.105%	$261.5189	$261.52	$261.50	$261.50
Purchase #4	$144.62	5.376%	$152.3948	$152.39	$152.40	$152.40
Purchase #5	$69.27	4.627%	$72.4751	$72.48	$72.50	$72.50
Purchase #6	$29.55	10.239%	$32.5756	$32.58	$32.60	$32.60
Purchase #7	$185.58	3.370%	$191.834	$191.83	$191.85	$191.80
7 purchase totals =	$922.78		$986.0122	$986.01	$986.05	$986.10