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	$169.75	6.516%	$180.8109	$180.81	$180.80	$180.80
Purchase #2	$72.76	10.609%	$80.4791	$80.48	$80.50	$80.50
Purchase #3	$194.75	13.427%	$220.8991	$220.90	$220.90	$220.90
Purchase #4	$72.68	8.133%	$78.5911	$78.59	$78.60	$78.60
Purchase #5	$40.82	13.731%	$46.425	$46.43	$46.45	$46.40
Purchase #6	$83.64	4.870%	$87.7133	$87.71	$87.70	$87.70
Purchase #7	$212.80	3.618%	$220.4991	$220.50	$220.50	$220.50
7 purchase totals =	$847.20		$915.4176	$915.42	$915.45	$915.40