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	$110.78	5.143%	$116.4774	$116.48	$116.50	$116.50
Purchase #2	$80.46	6.395%	$85.6054	$85.61	$85.60	$85.60
Purchase #3	$20.90	7.568%	$22.4817	$22.48	$22.50	$22.50
Purchase #4	$60.44	4.164%	$62.9567	$62.96	$62.95	$63.00
Purchase #5	$234.82	10.231%	$258.8444	$258.84	$258.85	$258.80
Purchase #6	$31.45	3.483%	$32.5454	$32.55	$32.55	$32.50
Purchase #7	$92.93	6.296%	$98.7809	$98.78	$98.80	$98.80
7 purchase totals =	$631.78		$677.6919	$677.70	$677.75	$677.70