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	$59.53	13.792%	$67.7404	$67.74	$67.75	$67.70
Purchase #2	$219.25	13.293%	$248.3949	$248.39	$248.40	$248.40
Purchase #3	$18.90	11.438%	$21.0618	$21.06	$21.05	$21.10
Purchase #4	$54.68	8.666%	$59.4186	$59.42	$59.40	$59.40
Purchase #5	$51.39	3.524%	$53.201	$53.20	$53.20	$53.20
Purchase #6	$163.38	9.434%	$178.7933	$178.79	$178.80	$178.80
Purchase #7	$215.89	11.455%	$240.6202	$240.62	$240.60	$240.60
7 purchase totals =	$783.02		$869.2302	$869.22	$869.20	$869.20