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	$27.55	12.552%	$31.0081	$31.01	$31.00	$31.00
Purchase #2	$236.76	5.126%	$248.8963	$248.90	$248.90	$248.90
Purchase #3	$249.80	11.851%	$279.4038	$279.40	$279.40	$279.40
Purchase #4	$185.36	13.447%	$210.2854	$210.29	$210.30	$210.30
Purchase #5	$171.81	8.712%	$186.7781	$186.78	$186.80	$186.80
Purchase #6	$172.83	13.549%	$196.2467	$196.25	$196.25	$196.20
Purchase #7	$108.77	13.495%	$123.4485	$123.45	$123.45	$123.40
7 purchase totals =	$1,152.88		$1,276.0669	$1,276.08	$1,276.10	$1,276.00