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	$125.80	8.702%	$136.7471	$136.75	$136.75	$136.70
Purchase #2	$65.64	13.518%	$74.5132	$74.51	$74.50	$74.50
Purchase #3	$90.90	10.511%	$100.4545	$100.45	$100.45	$100.50
Purchase #4	$57.32	7.147%	$61.4167	$61.42	$61.40	$61.40
Purchase #5	$173.83	5.690%	$183.7209	$183.72	$183.70	$183.70
Purchase #6	$25.35	8.545%	$27.5162	$27.52	$27.50	$27.50
Purchase #7	$6.86	5.312%	$7.2244	$7.22	$7.20	$7.20
7 purchase totals =	$545.70		$591.5930	$591.59	$591.50	$591.50