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	$35.54	13.758%	$40.4296	$40.43	$40.45	$40.40
Purchase #2	$61.93	3.539%	$64.1217	$64.12	$64.10	$64.10
Purchase #3	$238.40	11.210%	$265.1246	$265.12	$265.10	$265.10
Purchase #4	$10.56	12.509%	$11.881	$11.88	$11.90	$11.90
Purchase #5	$143.50	9.388%	$156.9718	$156.97	$156.95	$157.00
Purchase #6	$87.27	6.218%	$92.6964	$92.70	$92.70	$92.70
Purchase #7	$72.56	9.613%	$79.5352	$79.54	$79.55	$79.50
7 purchase totals =	$649.76		$710.7603	$710.76	$710.75	$710.70