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	$91.52	8.160%	$98.988	$98.99	$99.00	$99.00
Purchase #2	$167.78	11.509%	$187.0898	$187.09	$187.10	$187.10
Purchase #3	$97.28	4.488%	$101.6459	$101.65	$101.65	$101.60
Purchase #4	$178.50	12.492%	$200.7982	$200.80	$200.80	$200.80
Purchase #5	$132.42	7.123%	$141.8523	$141.85	$141.85	$141.90
Purchase #6	$189.48	5.828%	$200.5229	$200.52	$200.50	$200.50
Purchase #7	$14.73	5.464%	$15.5348	$15.53	$15.55	$15.50
7 purchase totals =	$871.71		$946.4319	$946.43	$946.45	$946.40