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	$19.65	4.165%	$20.4684	$20.47	$20.45	$20.50
Purchase #2	$48.92	4.144%	$50.9472	$50.95	$50.95	$50.90
Purchase #3	$122.25	13.710%	$139.0105	$139.01	$139.00	$139.00
Purchase #4	$234.50	9.678%	$257.1949	$257.19	$257.20	$257.20
Purchase #5	$37.59	4.108%	$39.1342	$39.13	$39.15	$39.10
Purchase #6	$127.76	8.746%	$138.9339	$138.93	$138.95	$138.90
Purchase #7	$132.74	13.630%	$150.8325	$150.83	$150.85	$150.80
7 purchase totals =	$723.41		$796.5216	$796.51	$796.55	$796.40