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	$23.30	5.739%	$24.6372	$24.64	$24.65	$24.60
Purchase #2	$217.29	6.340%	$231.0662	$231.07	$231.05	$231.10
Purchase #3	$102.56	8.706%	$111.4889	$111.49	$111.50	$111.50
Purchase #4	$207.59	3.438%	$214.7269	$214.73	$214.75	$214.70
Purchase #5	$166.77	5.224%	$175.4821	$175.48	$175.50	$175.50
Purchase #6	$119.48	6.698%	$127.4828	$127.48	$127.50	$127.50
Purchase #7	$22.38	11.151%	$24.8756	$24.88	$24.90	$24.90
7 purchase totals =	$859.37		$909.7597	$909.77	$909.85	$909.80