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	$121.56	8.462%	$131.8464	$131.85	$131.85	$131.80
Purchase #2	$29.38	6.858%	$31.3949	$31.39	$31.40	$31.40
Purchase #3	$103.83	8.677%	$112.8393	$112.84	$112.85	$112.80
Purchase #4	$30.74	10.256%	$33.8927	$33.89	$33.90	$33.90
Purchase #5	$194.67	12.690%	$219.3736	$219.37	$219.35	$219.40
Purchase #6	$47.40	7.228%	$50.8261	$50.83	$50.85	$50.80
Purchase #7	$146.79	5.252%	$154.4994	$154.50	$154.50	$154.50
7 purchase totals =	$674.37		$734.6724	$734.67	$734.70	$734.60