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	$43.62	5.482%	$46.0112	$46.01	$46.00	$46.00
Purchase #2	$138.90	4.544%	$145.2116	$145.21	$145.20	$145.20
Purchase #3	$52.55	13.291%	$59.5344	$59.53	$59.55	$59.50
Purchase #4	$116.48	13.204%	$131.86	$131.86	$131.85	$131.90
Purchase #5	$143.86	4.323%	$150.0791	$150.08	$150.10	$150.10
Purchase #6	$57.57	11.423%	$64.1462	$64.15	$64.15	$64.10
Purchase #7	$40.93	6.474%	$43.5798	$43.58	$43.60	$43.60
7 purchase totals =	$593.91		$640.4223	$640.42	$640.45	$640.40