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	$26.25	13.633%	$29.8287	$29.83	$29.85	$29.80
Purchase #2	$87.39	3.213%	$90.1978	$90.20	$90.20	$90.20
Purchase #3	$142.84	9.660%	$156.6383	$156.64	$156.65	$156.60
Purchase #4	$171.80	10.733%	$190.2393	$190.24	$190.25	$190.20
Purchase #5	$40.32	7.268%	$43.2505	$43.25	$43.25	$43.30
Purchase #6	$83.70	3.778%	$86.8622	$86.86	$86.85	$86.90
Purchase #7	$27.51	5.196%	$28.9394	$28.94	$28.95	$28.90
7 purchase totals =	$579.81		$625.9562	$625.96	$626.00	$625.90