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	$10.77	12.139%	$12.0774	$12.08	$12.10	$12.10
Purchase #2	$111.27	8.715%	$120.9672	$120.97	$120.95	$121.00
Purchase #3	$49.93	7.191%	$53.5205	$53.52	$53.50	$53.50
Purchase #4	$93.87	13.189%	$106.2505	$106.25	$106.25	$106.30
Purchase #5	$167.89	7.457%	$180.4096	$180.41	$180.40	$180.40
Purchase #6	$155.52	5.773%	$164.4982	$164.50	$164.50	$164.50
Purchase #7	$159.89	5.125%	$168.0844	$168.08	$168.10	$168.10
7 purchase totals =	$749.14		$805.8078	$805.81	$805.80	$805.90