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	$106.38	10.824%	$117.8946	$117.89	$117.90	$117.90
Purchase #2	$248.94	12.167%	$279.2285	$279.23	$279.25	$279.20
Purchase #3	$208.43	3.756%	$216.2586	$216.26	$216.25	$216.30
Purchase #4	$176.66	4.294%	$184.2458	$184.25	$184.25	$184.20
Purchase #5	$182.77	12.652%	$205.8941	$205.89	$205.90	$205.90
Purchase #6	$164.40	3.395%	$169.9814	$169.98	$170.00	$170.00
Purchase #7	$21.69	7.356%	$23.2855	$23.29	$23.30	$23.30
7 purchase totals =	$1,109.27		$1,196.7885	$1,196.79	$1,196.85	$1,196.80