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	$11.99	7.272%	$12.8619	$12.86	$12.85	$12.90
Purchase #2	$174.50	11.570%	$194.6897	$194.69	$194.70	$194.70
Purchase #3	$194.59	10.447%	$214.9188	$214.92	$214.90	$214.90
Purchase #4	$198.85	5.840%	$210.4628	$210.46	$210.45	$210.50
Purchase #5	$69.32	13.636%	$78.7725	$78.77	$78.75	$78.80
Purchase #6	$227.55	9.395%	$248.9283	$248.93	$248.95	$248.90
Purchase #7	$38.32	6.606%	$40.8514	$40.85	$40.85	$40.90
7 purchase totals =	$915.12		$1,001.4854	$1,001.48	$1,001.45	$1,001.60