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	$96.66	13.391%	$109.6037	$109.60	$109.60	$109.60
Purchase #2	$184.83	10.718%	$204.6401	$204.64	$204.65	$204.60
Purchase #3	$102.75	13.288%	$116.4034	$116.40	$116.40	$116.40
Purchase #4	$124.86	11.527%	$139.2526	$139.25	$139.25	$139.30
Purchase #5	$39.32	11.810%	$43.9637	$43.96	$43.95	$44.00
Purchase #6	$126.95	13.867%	$144.5542	$144.55	$144.55	$144.60
Purchase #7	$15.48	13.453%	$17.5625	$17.56	$17.55	$17.60
7 purchase totals =	$690.85		$775.9802	$775.96	$775.95	$776.10