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	$28.38	4.262%	$29.5896	$29.59	$29.60	$29.60
Purchase #2	$127.38	7.508%	$136.9437	$136.94	$136.95	$136.90
Purchase #3	$193.95	5.826%	$205.2495	$205.25	$205.25	$205.20
Purchase #4	$48.78	8.385%	$52.8702	$52.87	$52.85	$52.90
Purchase #5	$175.91	9.432%	$192.5018	$192.50	$192.50	$192.50
Purchase #6	$178.46	6.235%	$189.587	$189.59	$189.60	$189.60
Purchase #7	$78.81	5.808%	$83.3873	$83.39	$83.40	$83.40
7 purchase totals =	$831.67		$890.1291	$890.13	$890.15	$890.10