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	$21.64	13.295%	$24.517	$24.52	$24.50	$24.50
Purchase #2	$16.92	4.248%	$17.6388	$17.64	$17.65	$17.60
Purchase #3	$127.62	12.794%	$143.9477	$143.95	$143.95	$143.90
Purchase #4	$84.44	7.629%	$90.8819	$90.88	$90.90	$90.90
Purchase #5	$178.56	11.320%	$198.773	$198.77	$198.75	$198.80
Purchase #6	$228.62	11.835%	$255.6772	$255.68	$255.70	$255.70
Purchase #7	$40.30	6.282%	$42.8316	$42.83	$42.85	$42.80
7 purchase totals =	$698.10		$774.2672	$774.27	$774.30	$774.20