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	$38.40	5.856%	$40.6487	$40.65	$40.65	$40.60
Purchase #2	$56.61	11.792%	$63.2855	$63.29	$63.30	$63.30
Purchase #3	$108.60	9.241%	$118.6357	$118.64	$118.65	$118.60
Purchase #4	$109.50	10.844%	$121.3742	$121.37	$121.35	$121.40
Purchase #5	$161.35	3.344%	$166.7455	$166.75	$166.75	$166.70
Purchase #6	$31.63	13.573%	$35.9231	$35.92	$35.90	$35.90
Purchase #7	$96.41	4.253%	$100.5103	$100.51	$100.50	$100.50
7 purchase totals =	$602.50		$647.1230	$647.13	$647.10	$647.00