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	$10.56	8.717%	$11.4805	$11.48	$11.50	$11.50
Purchase #2	$193.29	12.158%	$216.7902	$216.79	$216.80	$216.80
Purchase #3	$103.99	12.506%	$116.995	$117.00	$117.00	$117.00
Purchase #4	$250.26	13.839%	$284.8935	$284.89	$284.90	$284.90
Purchase #5	$213.95	11.497%	$238.5478	$238.55	$238.55	$238.50
Purchase #6	$18.94	12.713%	$21.3478	$21.35	$21.35	$21.30
Purchase #7	$215.59	8.234%	$233.3417	$233.34	$233.35	$233.30
7 purchase totals =	$1,006.58		$1,123.3965	$1,123.40	$1,123.45	$1,123.30