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	$123.84	13.752%	$140.8705	$140.87	$140.85	$140.90
Purchase #2	$131.32	12.375%	$147.5709	$147.57	$147.55	$147.60
Purchase #3	$18.94	13.189%	$21.438	$21.44	$21.45	$21.40
Purchase #4	$248.89	6.718%	$265.6104	$265.61	$265.60	$265.60
Purchase #5	$123.97	3.489%	$128.2953	$128.30	$128.30	$128.30
Purchase #6	$102.48	9.664%	$112.3837	$112.38	$112.40	$112.40
Purchase #7	$151.98	6.652%	$162.0897	$162.09	$162.10	$162.10
7 purchase totals =	$901.42		$978.2585	$978.26	$978.25	$978.30