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	$46.31	8.588%	$50.2871	$50.29	$50.30	$50.30
Purchase #2	$231.31	8.300%	$250.5087	$250.51	$250.50	$250.50
Purchase #3	$198.44	12.197%	$222.6437	$222.64	$222.65	$222.60
Purchase #4	$40.53	12.785%	$45.7118	$45.71	$45.70	$45.70
Purchase #5	$13.46	11.546%	$15.0141	$15.01	$15.00	$15.00
Purchase #6	$43.61	6.733%	$46.5463	$46.55	$46.55	$46.50
Purchase #7	$30.80	13.606%	$34.9906	$34.99	$35.00	$35.00
7 purchase totals =	$604.46		$665.7023	$665.70	$665.70	$665.60