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	$34.31	3.416%	$35.482	$35.48	$35.50	$35.50
Purchase #2	$146.59	6.773%	$156.5185	$156.52	$156.50	$156.50
Purchase #3	$101.50	3.259%	$104.8079	$104.81	$104.80	$104.80
Purchase #4	$36.46	5.505%	$38.4671	$38.47	$38.45	$38.50
Purchase #5	$40.31	7.563%	$43.3586	$43.36	$43.35	$43.40
Purchase #6	$223.48	7.466%	$240.165	$240.17	$240.15	$240.20
Purchase #7	$222.60	8.521%	$241.5677	$241.57	$241.55	$241.60
7 purchase totals =	$805.25		$860.3668	$860.38	$860.30	$860.50