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	$84.56	6.536%	$90.0868	$90.09	$90.10	$90.10
Purchase #2	$144.99	11.652%	$161.8842	$161.88	$161.90	$161.90
Purchase #3	$123.64	13.629%	$140.4909	$140.49	$140.50	$140.50
Purchase #4	$163.62	13.340%	$185.4469	$185.45	$185.45	$185.40
Purchase #5	$107.60	7.810%	$116.0036	$116.00	$116.00	$116.00
Purchase #6	$39.58	10.799%	$43.8542	$43.85	$43.85	$43.90
Purchase #7	$54.93	12.147%	$61.6023	$61.60	$61.60	$61.60
7 purchase totals =	$718.92		$799.3689	$799.36	$799.40	$799.40