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	$57.79	8.162%	$62.5068	$62.51	$62.50	$62.50
Purchase #2	$109.39	9.118%	$119.3642	$119.36	$119.35	$119.40
Purchase #3	$192.42	8.525%	$208.8238	$208.82	$208.80	$208.80
Purchase #4	$187.47	8.844%	$204.0498	$204.05	$204.05	$204.00
Purchase #5	$80.98	10.603%	$89.5663	$89.57	$89.55	$89.60
Purchase #6	$146.89	6.452%	$156.3673	$156.37	$156.35	$156.40
Purchase #7	$125.59	12.630%	$141.452	$141.45	$141.45	$141.50
7 purchase totals =	$900.53		$982.1302	$982.13	$982.05	$982.20