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	$47.41	4.466%	$49.5273	$49.53	$49.55	$49.50
Purchase #2	$35.95	5.193%	$37.8169	$37.82	$37.80	$37.80
Purchase #3	$115.93	13.490%	$131.569	$131.57	$131.55	$131.60
Purchase #4	$123.48	7.287%	$132.478	$132.48	$132.50	$132.50
Purchase #5	$127.40	10.352%	$140.5884	$140.59	$140.60	$140.60
Purchase #6	$231.35	12.159%	$259.4798	$259.48	$259.50	$259.50
Purchase #7	$105.54	3.598%	$109.3373	$109.34	$109.35	$109.30
7 purchase totals =	$787.06		$860.7967	$860.81	$860.85	$860.80