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	$248.47	12.430%	$279.3548	$279.35	$279.35	$279.40
Purchase #2	$131.71	5.124%	$138.4588	$138.46	$138.45	$138.50
Purchase #3	$68.54	4.751%	$71.7963	$71.80	$71.80	$71.80
Purchase #4	$40.80	10.650%	$45.1452	$45.15	$45.15	$45.10
Purchase #5	$187.58	3.874%	$194.8468	$194.85	$194.85	$194.80
Purchase #6	$123.30	10.709%	$136.5042	$136.50	$136.50	$136.50
Purchase #7	$212.76	9.762%	$233.5296	$233.53	$233.55	$233.50
7 purchase totals =	$1,013.16		$1,099.6357	$1,099.64	$1,099.65	$1,099.60