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	$6.89	5.510%	$7.2696	$7.27	$7.25	$7.30
Purchase #2	$132.87	6.850%	$141.9716	$141.97	$141.95	$142.00
Purchase #3	$193.93	13.665%	$220.4305	$220.43	$220.45	$220.40
Purchase #4	$197.35	9.370%	$215.8417	$215.84	$215.85	$215.80
Purchase #5	$132.65	4.838%	$139.0676	$139.07	$139.05	$139.10
Purchase #6	$102.29	10.363%	$112.8903	$112.89	$112.90	$112.90
Purchase #7	$88.63	7.785%	$95.5298	$95.53	$95.55	$95.50
7 purchase totals =	$854.61		$933.0011	$933.00	$933.00	$933.00