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	$126.70	6.141%	$134.4806	$134.48	$134.50	$134.50
Purchase #2	$62.74	13.777%	$71.3837	$71.38	$71.40	$71.40
Purchase #3	$246.43	5.315%	$259.5278	$259.53	$259.55	$259.50
Purchase #4	$147.56	3.777%	$153.1333	$153.13	$153.15	$153.10
Purchase #5	$144.73	7.832%	$156.0653	$156.07	$156.05	$156.10
Purchase #6	$171.72	11.733%	$191.8679	$191.87	$191.85	$191.90
Purchase #7	$215.72	3.166%	$222.5497	$222.55	$222.55	$222.50
7 purchase totals =	$1,115.60		$1,189.0083	$1,189.01	$1,189.05	$1,189.00