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	$123.68	7.116%	$132.4811	$132.48	$132.50	$132.50
Purchase #2	$72.40	10.388%	$79.9209	$79.92	$79.90	$79.90
Purchase #3	$226.95	7.693%	$244.4093	$244.41	$244.40	$244.40
Purchase #4	$63.63	4.712%	$66.6282	$66.63	$66.65	$66.60
Purchase #5	$241.82	9.831%	$265.5933	$265.59	$265.60	$265.60
Purchase #6	$82.72	6.201%	$87.8495	$87.85	$87.85	$87.80
Purchase #7	$41.46	10.277%	$45.7208	$45.72	$45.70	$45.70
7 purchase totals =	$852.66		$922.6031	$922.60	$922.60	$922.50