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	$12.45	10.859%	$13.8019	$13.80	$13.80	$13.80
Purchase #2	$61.34	8.653%	$66.6478	$66.65	$66.65	$66.60
Purchase #3	$53.73	3.503%	$55.6122	$55.61	$55.60	$55.60
Purchase #4	$176.25	6.696%	$188.0517	$188.05	$188.05	$188.10
Purchase #5	$223.47	3.599%	$231.5127	$231.51	$231.50	$231.50
Purchase #6	$237.51	8.557%	$257.8337	$257.83	$257.85	$257.80
Purchase #7	$156.54	5.348%	$164.9118	$164.91	$164.90	$164.90
7 purchase totals =	$921.29		$978.3718	$978.36	$978.35	$978.30