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	$212.99	12.131%	$238.8278	$238.83	$238.85	$238.80
Purchase #2	$133.64	5.638%	$141.1746	$141.17	$141.15	$141.20
Purchase #3	$130.25	8.722%	$141.6104	$141.61	$141.60	$141.60
Purchase #4	$18.72	9.723%	$20.5401	$20.54	$20.55	$20.50
Purchase #5	$226.48	3.866%	$235.2357	$235.24	$235.25	$235.20
Purchase #6	$156.51	5.287%	$164.7847	$164.78	$164.80	$164.80
Purchase #7	$145.58	8.798%	$158.3881	$158.39	$158.40	$158.40
7 purchase totals =	$1,024.17		$1,100.5614	$1,100.56	$1,100.60	$1,100.50