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	$48.80	11.814%	$54.5652	$54.57	$54.55	$54.60
Purchase #2	$42.98	11.528%	$47.9347	$47.93	$47.95	$47.90
Purchase #3	$181.74	10.322%	$200.4992	$200.50	$200.50	$200.50
Purchase #4	$59.25	7.355%	$63.6078	$63.61	$63.60	$63.60
Purchase #5	$42.27	8.400%	$45.8207	$45.82	$45.80	$45.80
Purchase #6	$199.93	9.509%	$218.9413	$218.94	$218.95	$218.90
Purchase #7	$113.61	4.699%	$118.9485	$118.95	$118.95	$118.90
7 purchase totals =	$688.58		$750.3174	$750.32	$750.30	$750.20