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	$19.45	6.509%	$20.716	$20.72	$20.70	$20.70
Purchase #2	$128.77	8.199%	$139.3279	$139.33	$139.35	$139.30
Purchase #3	$63.92	4.233%	$66.6257	$66.63	$66.65	$66.60
Purchase #4	$48.27	5.854%	$51.0957	$51.10	$51.10	$51.10
Purchase #5	$200.48	13.688%	$227.9217	$227.92	$227.90	$227.90
Purchase #6	$231.32	11.243%	$257.3273	$257.33	$257.35	$257.30
Purchase #7	$59.25	3.384%	$61.255	$61.26	$61.25	$61.30
7 purchase totals =	$751.46		$824.2693	$824.29	$824.30	$824.20