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	$123.39	13.171%	$139.6417	$139.64	$139.65	$139.60
Purchase #2	$59.66	6.723%	$63.6709	$63.67	$63.65	$63.70
Purchase #3	$128.99	11.505%	$143.8303	$143.83	$143.85	$143.80
Purchase #4	$137.57	3.350%	$142.1786	$142.18	$142.20	$142.20
Purchase #5	$110.37	12.167%	$123.7987	$123.80	$123.80	$123.80
Purchase #6	$54.86	13.847%	$62.4565	$62.46	$62.45	$62.50
Purchase #7	$127.49	10.163%	$140.4468	$140.45	$140.45	$140.40
7 purchase totals =	$742.33		$816.0235	$816.03	$816.05	$816.00