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	$9.40	5.242%	$9.8927	$9.89	$9.90	$9.90
Purchase #2	$95.67	5.363%	$100.8008	$100.80	$100.80	$100.80
Purchase #3	$176.48	5.214%	$185.6817	$185.68	$185.70	$185.70
Purchase #4	$127.61	6.625%	$136.0642	$136.06	$136.05	$136.10
Purchase #5	$167.81	10.737%	$185.8278	$185.83	$185.85	$185.80
Purchase #6	$117.80	13.168%	$133.3119	$133.31	$133.30	$133.30
Purchase #7	$133.85	10.491%	$147.8922	$147.89	$147.90	$147.90
7 purchase totals =	$828.62		$899.4713	$899.46	$899.50	$899.50