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	$80.84	12.333%	$90.81	$90.81	$90.80	$90.80
Purchase #2	$17.27	7.668%	$18.5943	$18.59	$18.60	$18.60
Purchase #3	$138.42	7.314%	$148.544	$148.54	$148.55	$148.50
Purchase #4	$8.76	12.319%	$9.8391	$9.84	$9.85	$9.80
Purchase #5	$228.54	10.131%	$251.6934	$251.69	$251.70	$251.70
Purchase #6	$248.25	9.806%	$272.5934	$272.59	$272.60	$272.60
Purchase #7	$154.47	6.524%	$164.5476	$164.55	$164.55	$164.50
7 purchase totals =	$876.55		$956.6218	$956.61	$956.65	$956.50