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	$35.88	13.701%	$40.7959	$40.80	$40.80	$40.80
Purchase #2	$75.49	8.487%	$81.8968	$81.90	$81.90	$81.90
Purchase #3	$198.43	5.149%	$208.6472	$208.65	$208.65	$208.60
Purchase #4	$133.83	4.316%	$139.6061	$139.61	$139.60	$139.60
Purchase #5	$131.59	6.629%	$140.3131	$140.31	$140.30	$140.30
Purchase #6	$209.89	7.440%	$225.5058	$225.51	$225.50	$225.50
Purchase #7	$229.66	13.357%	$260.3357	$260.34	$260.35	$260.30
7 purchase totals =	$1,014.77		$1,097.1006	$1,097.12	$1,097.10	$1,097.00