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	$74.30	6.218%	$78.92	$78.92	$78.90	$78.90
Purchase #2	$228.86	11.360%	$254.8585	$254.86	$254.85	$254.90
Purchase #3	$12.93	4.461%	$13.5068	$13.51	$13.50	$13.50
Purchase #4	$244.58	5.353%	$257.6724	$257.67	$257.65	$257.70
Purchase #5	$14.27	5.509%	$15.0561	$15.06	$15.05	$15.10
Purchase #6	$38.99	3.250%	$40.2572	$40.26	$40.25	$40.30
Purchase #7	$80.45	3.763%	$83.4773	$83.48	$83.50	$83.50
7 purchase totals =	$694.38		$743.7483	$743.76	$743.70	$743.90