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	$75.36	13.675%	$85.6655	$85.67	$85.65	$85.70
Purchase #2	$63.92	6.278%	$67.9329	$67.93	$67.95	$67.90
Purchase #3	$231.35	4.446%	$241.6358	$241.64	$241.65	$241.60
Purchase #4	$84.41	8.730%	$91.779	$91.78	$91.80	$91.80
Purchase #5	$116.33	13.346%	$131.8554	$131.86	$131.85	$131.90
Purchase #6	$111.71	13.173%	$126.4256	$126.43	$126.45	$126.40
Purchase #7	$85.38	10.703%	$94.5182	$94.52	$94.50	$94.50
7 purchase totals =	$768.46		$839.8124	$839.83	$839.85	$839.80