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	$104.45	11.421%	$116.3792	$116.38	$116.40	$116.40
Purchase #2	$230.60	12.492%	$259.4066	$259.41	$259.40	$259.40
Purchase #3	$156.80	13.709%	$178.2957	$178.30	$178.30	$178.30
Purchase #4	$152.90	12.500%	$172.0125	$172.01	$172.00	$172.00
Purchase #5	$161.63	10.306%	$178.2876	$178.29	$178.30	$178.30
Purchase #6	$19.82	10.674%	$21.9356	$21.94	$21.95	$21.90
Purchase #7	$139.25	11.192%	$154.8349	$154.83	$154.85	$154.80
7 purchase totals =	$965.45		$1,081.1521	$1,081.16	$1,081.20	$1,081.10