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	$14.77	5.414%	$15.5696	$15.57	$15.55	$15.60
Purchase #2	$102.85	11.432%	$114.6078	$114.61	$114.60	$114.60
Purchase #3	$158.58	3.502%	$164.1335	$164.13	$164.15	$164.10
Purchase #4	$102.43	13.855%	$116.6217	$116.62	$116.60	$116.60
Purchase #5	$184.37	8.611%	$200.2461	$200.25	$200.25	$200.20
Purchase #6	$40.67	7.241%	$43.6149	$43.61	$43.60	$43.60
Purchase #7	$128.65	12.372%	$144.5666	$144.57	$144.55	$144.60
7 purchase totals =	$732.32		$799.3602	$799.36	$799.30	$799.30