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	$239.67	6.517%	$255.2893	$255.29	$255.30	$255.30
Purchase #2	$79.61	5.109%	$83.6773	$83.68	$83.70	$83.70
Purchase #3	$102.34	13.782%	$116.4445	$116.44	$116.45	$116.40
Purchase #4	$117.29	6.699%	$125.1473	$125.15	$125.15	$125.10
Purchase #5	$127.47	10.690%	$141.0965	$141.10	$141.10	$141.10
Purchase #6	$87.51	10.179%	$96.4176	$96.42	$96.40	$96.40
Purchase #7	$90.87	11.718%	$101.5181	$101.52	$101.50	$101.50
7 purchase totals =	$844.76		$919.5906	$919.60	$919.60	$919.50