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	$97.29	5.540%	$102.6799	$102.68	$102.70	$102.70
Purchase #2	$185.60	10.182%	$204.4978	$204.50	$204.50	$204.50
Purchase #3	$162.65	8.167%	$175.9336	$175.93	$175.95	$175.90
Purchase #4	$117.57	12.548%	$132.3227	$132.32	$132.30	$132.30
Purchase #5	$118.55	10.577%	$131.089	$131.09	$131.10	$131.10
Purchase #6	$98.85	12.676%	$111.3802	$111.38	$111.40	$111.40
Purchase #7	$29.27	8.818%	$31.851	$31.85	$31.85	$31.90
7 purchase totals =	$809.78		$889.7542	$889.75	$889.80	$889.80