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	$103.80	12.554%	$116.8311	$116.83	$116.85	$116.80
Purchase #2	$208.72	8.574%	$226.6157	$226.62	$226.60	$226.60
Purchase #3	$208.59	13.711%	$237.1898	$237.19	$237.20	$237.20
Purchase #4	$201.69	5.567%	$212.9181	$212.92	$212.90	$212.90
Purchase #5	$91.86	9.119%	$100.2367	$100.24	$100.25	$100.20
Purchase #6	$50.90	12.733%	$57.3811	$57.38	$57.40	$57.40
Purchase #7	$52.25	4.633%	$54.6707	$54.67	$54.65	$54.70
7 purchase totals =	$917.81		$1,005.8432	$1,005.85	$1,005.85	$1,005.80