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	$232.68	10.839%	$257.9002	$257.90	$257.90	$257.90
Purchase #2	$200.87	11.703%	$224.3778	$224.38	$224.40	$224.40
Purchase #3	$249.92	12.280%	$280.6102	$280.61	$280.60	$280.60
Purchase #4	$165.83	7.860%	$178.8642	$178.86	$178.85	$178.90
Purchase #5	$165.25	5.106%	$173.6877	$173.69	$173.70	$173.70
Purchase #6	$51.51	9.682%	$56.4972	$56.50	$56.50	$56.50
Purchase #7	$56.43	6.171%	$59.9123	$59.91	$59.90	$59.90
7 purchase totals =	$1,122.49		$1,231.8496	$1,231.85	$1,231.85	$1,231.90