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	$35.63	6.663%	$38.004	$38.00	$38.00	$38.00
Purchase #2	$227.82	6.262%	$242.0861	$242.09	$242.10	$242.10
Purchase #3	$209.70	7.690%	$225.8259	$225.83	$225.85	$225.80
Purchase #4	$238.80	10.503%	$263.8812	$263.88	$263.90	$263.90
Purchase #5	$40.88	13.697%	$46.4793	$46.48	$46.50	$46.50
Purchase #6	$9.86	5.712%	$10.4232	$10.42	$10.40	$10.40
Purchase #7	$159.47	12.798%	$179.879	$179.88	$179.90	$179.90
7 purchase totals =	$922.16		$1,006.5787	$1,006.58	$1,006.65	$1,006.60