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	$140.72	12.849%	$158.8011	$158.80	$158.80	$158.80
Purchase #2	$175.82	11.836%	$196.6301	$196.63	$196.65	$196.60
Purchase #3	$37.92	9.439%	$41.4993	$41.50	$41.50	$41.50
Purchase #4	$165.95	9.390%	$181.5327	$181.53	$181.55	$181.50
Purchase #5	$246.33	5.252%	$259.2673	$259.27	$259.25	$259.30
Purchase #6	$125.43	13.167%	$141.9454	$141.95	$141.95	$141.90
Purchase #7	$214.84	8.529%	$233.1637	$233.16	$233.15	$233.20
7 purchase totals =	$1,107.01		$1,212.8396	$1,212.84	$1,212.85	$1,212.80