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	$23.36	9.249%	$25.5206	$25.52	$25.50	$25.50
Purchase #2	$104.30	13.573%	$118.4566	$118.46	$118.45	$118.50
Purchase #3	$61.98	9.230%	$67.7008	$67.70	$67.70	$67.70
Purchase #4	$43.59	4.567%	$45.5808	$45.58	$45.60	$45.60
Purchase #5	$168.83	5.416%	$177.9738	$177.97	$177.95	$178.00
Purchase #6	$139.38	6.591%	$148.5665	$148.57	$148.55	$148.60
Purchase #7	$173.98	3.103%	$179.3786	$179.38	$179.40	$179.40
7 purchase totals =	$715.42		$763.1777	$763.18	$763.15	$763.30