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	$200.69	8.380%	$217.5078	$217.51	$217.50	$217.50
Purchase #2	$122.29	8.364%	$132.5183	$132.52	$132.50	$132.50
Purchase #3	$126.98	9.834%	$139.4672	$139.47	$139.45	$139.50
Purchase #4	$140.57	11.286%	$156.4347	$156.43	$156.45	$156.40
Purchase #5	$193.58	13.509%	$219.7307	$219.73	$219.75	$219.70
Purchase #6	$136.96	4.589%	$143.2451	$143.25	$143.25	$143.20
Purchase #7	$213.41	4.274%	$222.5311	$222.53	$222.55	$222.50
7 purchase totals =	$1,134.48		$1,231.4349	$1,231.44	$1,231.45	$1,231.30