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	$37.50	8.865%	$40.8244	$40.82	$40.80	$40.80
Purchase #2	$131.47	7.646%	$141.5222	$141.52	$141.50	$141.50
Purchase #3	$80.83	8.472%	$87.6779	$87.68	$87.70	$87.70
Purchase #4	$149.43	3.518%	$154.6869	$154.69	$154.70	$154.70
Purchase #5	$131.96	8.158%	$142.7253	$142.73	$142.75	$142.70
Purchase #6	$132.78	3.553%	$137.4977	$137.50	$137.50	$137.50
Purchase #7	$190.75	3.567%	$197.5541	$197.55	$197.55	$197.60
7 purchase totals =	$854.72		$902.4885	$902.49	$902.50	$902.50