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	$15.29	4.437%	$15.9684	$15.97	$15.95	$16.00
Purchase #2	$153.83	13.649%	$174.8263	$174.83	$174.85	$174.80
Purchase #3	$105.80	3.121%	$109.102	$109.10	$109.10	$109.10
Purchase #4	$199.95	11.331%	$222.6063	$222.61	$222.60	$222.60
Purchase #5	$80.50	5.700%	$85.0885	$85.09	$85.10	$85.10
Purchase #6	$50.63	7.577%	$54.4662	$54.47	$54.45	$54.50
Purchase #7	$162.41	8.735%	$176.5965	$176.60	$176.60	$176.60
7 purchase totals =	$768.41		$838.6542	$838.67	$838.65	$838.70