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	$232.97	9.824%	$255.857	$255.86	$255.85	$255.90
Purchase #2	$187.94	5.749%	$198.7447	$198.74	$198.75	$198.70
Purchase #3	$45.82	11.741%	$51.1997	$51.20	$51.20	$51.20
Purchase #4	$63.42	5.762%	$67.0743	$67.07	$67.05	$67.10
Purchase #5	$28.82	10.154%	$31.7464	$31.75	$31.75	$31.70
Purchase #6	$30.58	4.320%	$31.9011	$31.90	$31.90	$31.90
Purchase #7	$61.52	9.389%	$67.2961	$67.30	$67.30	$67.30
7 purchase totals =	$651.07		$703.8193	$703.82	$703.80	$703.80