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	$136.38	5.808%	$144.301	$144.30	$144.30	$144.30
Purchase #2	$76.28	9.775%	$83.7364	$83.74	$83.75	$83.70
Purchase #3	$150.63	10.595%	$166.5892	$166.59	$166.60	$166.60
Purchase #4	$154.26	13.742%	$175.4584	$175.46	$175.45	$175.50
Purchase #5	$29.64	6.638%	$31.6075	$31.61	$31.60	$31.60
Purchase #6	$152.70	7.778%	$164.577	$164.58	$164.60	$164.60
Purchase #7	$164.71	9.566%	$180.4662	$180.47	$180.45	$180.50
7 purchase totals =	$864.60		$946.7357	$946.75	$946.75	$946.80