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	$180.93	8.825%	$196.8971	$196.90	$196.90	$196.90
Purchase #2	$73.69	13.310%	$83.4981	$83.50	$83.50	$83.50
Purchase #3	$63.94	3.435%	$66.1363	$66.14	$66.15	$66.10
Purchase #4	$18.87	8.652%	$20.5026	$20.50	$20.50	$20.50
Purchase #5	$249.36	13.828%	$283.8415	$283.84	$283.85	$283.80
Purchase #6	$83.75	7.247%	$89.8194	$89.82	$89.80	$89.80
Purchase #7	$215.27	10.510%	$237.8949	$237.89	$237.90	$237.90
7 purchase totals =	$885.81		$978.5899	$978.59	$978.60	$978.50