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	$114.81	11.823%	$128.384	$128.38	$128.40	$128.40
Purchase #2	$158.91	10.390%	$175.4207	$175.42	$175.40	$175.40
Purchase #3	$172.86	10.235%	$190.5522	$190.55	$190.55	$190.60
Purchase #4	$147.89	12.604%	$166.5301	$166.53	$166.55	$166.50
Purchase #5	$45.65	4.239%	$47.5851	$47.59	$47.60	$47.60
Purchase #6	$66.60	4.843%	$69.8254	$69.83	$69.85	$69.80
Purchase #7	$16.53	9.405%	$18.0846	$18.08	$18.10	$18.10
7 purchase totals =	$723.25		$796.3821	$796.38	$796.45	$796.40