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	$241.27	7.334%	$258.9647	$258.96	$258.95	$259.00
Purchase #2	$132.50	9.382%	$144.9312	$144.93	$144.95	$144.90
Purchase #3	$36.61	11.254%	$40.7301	$40.73	$40.75	$40.70
Purchase #4	$170.94	13.548%	$194.099	$194.10	$194.10	$194.10
Purchase #5	$84.45	12.676%	$95.1549	$95.15	$95.15	$95.20
Purchase #6	$165.63	5.556%	$174.8324	$174.83	$174.85	$174.80
Purchase #7	$95.57	5.468%	$100.7958	$100.80	$100.80	$100.80
7 purchase totals =	$926.97		$1,009.5081	$1,009.50	$1,009.55	$1,009.50