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	$40.80	6.338%	$43.3859	$43.39	$43.40	$43.40
Purchase #2	$212.71	4.783%	$222.8839	$222.88	$222.90	$222.90
Purchase #3	$224.96	11.376%	$250.5514	$250.55	$250.55	$250.60
Purchase #4	$174.67	10.419%	$192.8689	$192.87	$192.85	$192.90
Purchase #5	$19.83	6.603%	$21.1394	$21.14	$21.15	$21.10
Purchase #6	$43.65	13.605%	$49.5886	$49.59	$49.60	$49.60
Purchase #7	$51.63	6.686%	$55.082	$55.08	$55.10	$55.10
7 purchase totals =	$768.25		$835.5001	$835.50	$835.55	$835.60