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	$36.96	8.482%	$40.0949	$40.09	$40.10	$40.10
Purchase #2	$230.72	7.577%	$248.2017	$248.20	$248.20	$248.20
Purchase #3	$126.57	3.602%	$131.1291	$131.13	$131.15	$131.10
Purchase #4	$66.55	7.139%	$71.301	$71.30	$71.30	$71.30
Purchase #5	$95.92	8.576%	$104.1461	$104.15	$104.15	$104.10
Purchase #6	$125.47	4.468%	$131.076	$131.08	$131.10	$131.10
Purchase #7	$238.69	4.707%	$249.9251	$249.93	$249.95	$249.90
7 purchase totals =	$920.88		$975.8739	$975.88	$975.95	$975.80