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	$65.29	10.583%	$72.1996	$72.20	$72.20	$72.20
Purchase #2	$59.86	4.395%	$62.4908	$62.49	$62.50	$62.50
Purchase #3	$171.54	8.842%	$186.7076	$186.71	$186.70	$186.70
Purchase #4	$188.82	12.419%	$212.2696	$212.27	$212.25	$212.30
Purchase #5	$86.83	5.436%	$91.5501	$91.55	$91.55	$91.60
Purchase #6	$87.93	4.402%	$91.8007	$91.80	$91.80	$91.80
Purchase #7	$56.54	9.387%	$61.8474	$61.85	$61.85	$61.80
7 purchase totals =	$716.81		$778.8658	$778.87	$778.85	$778.90