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	$101.28	7.595%	$108.9722	$108.97	$108.95	$109.00
Purchase #2	$99.57	6.175%	$105.7184	$105.72	$105.70	$105.70
Purchase #3	$138.39	4.105%	$144.0709	$144.07	$144.05	$144.10
Purchase #4	$209.67	13.712%	$238.42	$238.42	$238.40	$238.40
Purchase #5	$89.82	6.410%	$95.5775	$95.58	$95.60	$95.60
Purchase #6	$249.42	4.571%	$260.821	$260.82	$260.80	$260.80
Purchase #7	$44.53	4.138%	$46.3727	$46.37	$46.35	$46.40
7 purchase totals =	$932.68		$999.9527	$999.95	$999.85	$1,000.00