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	$90.82	7.583%	$97.7069	$97.71	$97.70	$97.70
Purchase #2	$83.65	9.828%	$91.8711	$91.87	$91.85	$91.90
Purchase #3	$78.51	13.562%	$89.1575	$89.16	$89.15	$89.20
Purchase #4	$250.43	11.765%	$279.8931	$279.89	$279.90	$279.90
Purchase #5	$109.88	5.189%	$115.5817	$115.58	$115.60	$115.60
Purchase #6	$32.92	11.795%	$36.8029	$36.80	$36.80	$36.80
Purchase #7	$132.66	5.127%	$139.4615	$139.46	$139.45	$139.50
7 purchase totals =	$778.87		$850.4747	$850.47	$850.45	$850.60