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	$250.76	11.446%	$279.462	$279.46	$279.45	$279.50
Purchase #2	$235.82	6.362%	$250.8229	$250.82	$250.80	$250.80
Purchase #3	$50.40	10.311%	$55.5967	$55.60	$55.60	$55.60
Purchase #4	$131.48	13.222%	$148.8643	$148.86	$148.85	$148.90
Purchase #5	$55.75	5.127%	$58.6083	$58.61	$58.60	$58.60
Purchase #6	$242.98	12.804%	$274.0912	$274.09	$274.10	$274.10
Purchase #7	$175.73	9.247%	$191.9798	$191.98	$192.00	$192.00
7 purchase totals =	$1,142.92		$1,259.4252	$1,259.42	$1,259.40	$1,259.50