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	$37.43	6.406%	$39.8278	$39.83	$39.85	$39.80
Purchase #2	$250.29	3.810%	$259.826	$259.83	$259.85	$259.80
Purchase #3	$114.94	8.575%	$124.7961	$124.80	$124.80	$124.80
Purchase #4	$148.30	9.521%	$162.4196	$162.42	$162.40	$162.40
Purchase #5	$48.62	7.471%	$52.2524	$52.25	$52.25	$52.30
Purchase #6	$244.29	7.504%	$262.6215	$262.62	$262.60	$262.60
Purchase #7	$86.30	4.396%	$90.0937	$90.09	$90.10	$90.10
7 purchase totals =	$930.17		$991.8371	$991.84	$991.85	$991.80