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	$12.61	6.137%	$13.3839	$13.38	$13.40	$13.40
Purchase #2	$130.51	7.293%	$140.0281	$140.03	$140.05	$140.00
Purchase #3	$84.70	9.119%	$92.4238	$92.42	$92.40	$92.40
Purchase #4	$34.27	3.414%	$35.44	$35.44	$35.45	$35.40
Purchase #5	$90.56	5.380%	$95.4321	$95.43	$95.45	$95.40
Purchase #6	$10.78	10.733%	$11.937	$11.94	$11.95	$11.90
Purchase #7	$59.92	13.130%	$67.7875	$67.79	$67.80	$67.80
7 purchase totals =	$423.35		$456.4324	$456.43	$456.50	$456.30