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	$35.86	13.683%	$40.7667	$40.77	$40.75	$40.80
Purchase #2	$135.30	12.691%	$152.4709	$152.47	$152.45	$152.50
Purchase #3	$224.42	7.742%	$241.7946	$241.79	$241.80	$241.80
Purchase #4	$185.69	6.835%	$198.3819	$198.38	$198.40	$198.40
Purchase #5	$53.34	11.326%	$59.3813	$59.38	$59.40	$59.40
Purchase #6	$28.72	12.719%	$32.3729	$32.37	$32.35	$32.40
Purchase #7	$233.64	10.425%	$257.997	$258.00	$258.00	$258.00
7 purchase totals =	$896.97		$983.1653	$983.16	$983.15	$983.30