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	$83.93	6.536%	$89.4157	$89.42	$89.40	$89.40
Purchase #2	$128.40	12.454%	$144.3909	$144.39	$144.40	$144.40
Purchase #3	$28.92	7.229%	$31.0106	$31.01	$31.00	$31.00
Purchase #4	$184.69	13.673%	$209.9427	$209.94	$209.95	$209.90
Purchase #5	$225.45	13.548%	$255.994	$255.99	$256.00	$256.00
Purchase #6	$21.29	7.856%	$22.9625	$22.96	$22.95	$23.00
Purchase #7	$9.95	9.665%	$10.9117	$10.91	$10.90	$10.90
7 purchase totals =	$682.63		$764.6281	$764.62	$764.60	$764.60