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	$59.34	9.846%	$65.1826	$65.18	$65.20	$65.20
Purchase #2	$54.32	8.863%	$59.1344	$59.13	$59.15	$59.10
Purchase #3	$111.29	5.340%	$117.2329	$117.23	$117.25	$117.20
Purchase #4	$53.85	11.151%	$59.8548	$59.85	$59.85	$59.90
Purchase #5	$116.40	13.263%	$131.8381	$131.84	$131.85	$131.80
Purchase #6	$97.54	4.712%	$102.1361	$102.14	$102.15	$102.10
Purchase #7	$132.33	12.204%	$148.4796	$148.48	$148.50	$148.50
7 purchase totals =	$625.07		$683.8585	$683.85	$683.95	$683.80