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	$231.89	5.836%	$245.4231	$245.42	$245.40	$245.40
Purchase #2	$75.48	3.511%	$78.1301	$78.13	$78.15	$78.10
Purchase #3	$45.54	13.560%	$51.7152	$51.72	$51.70	$51.70
Purchase #4	$245.38	11.733%	$274.1704	$274.17	$274.15	$274.20
Purchase #5	$97.83	4.120%	$101.8606	$101.86	$101.85	$101.90
Purchase #6	$44.53	9.358%	$48.6971	$48.70	$48.70	$48.70
Purchase #7	$113.40	11.529%	$126.4739	$126.47	$126.45	$126.50
7 purchase totals =	$854.05		$926.4704	$926.47	$926.40	$926.50