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	$89.40	12.487%	$100.5634	$100.56	$100.55	$100.60
Purchase #2	$108.81	13.833%	$123.8617	$123.86	$123.85	$123.90
Purchase #3	$197.36	10.136%	$217.3644	$217.36	$217.35	$217.40
Purchase #4	$214.60	13.262%	$243.0603	$243.06	$243.05	$243.10
Purchase #5	$47.42	10.170%	$52.2426	$52.24	$52.25	$52.20
Purchase #6	$110.85	13.623%	$125.9511	$125.95	$125.95	$126.00
Purchase #7	$111.71	6.783%	$119.2873	$119.29	$119.30	$119.30
7 purchase totals =	$880.15		$982.3308	$982.32	$982.30	$982.50