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	$90.41	10.555%	$99.9528	$99.95	$99.95	$100.00
Purchase #2	$144.57	8.474%	$156.8209	$156.82	$156.80	$156.80
Purchase #3	$144.35	4.491%	$150.8328	$150.83	$150.85	$150.80
Purchase #4	$62.96	7.303%	$67.558	$67.56	$67.55	$67.60
Purchase #5	$165.43	5.171%	$173.9844	$173.98	$174.00	$174.00
Purchase #6	$177.87	9.335%	$194.4742	$194.47	$194.45	$194.50
Purchase #7	$225.55	13.303%	$255.5549	$255.55	$255.55	$255.60
7 purchase totals =	$1,011.14		$1,099.1780	$1,099.16	$1,099.15	$1,099.30