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	$135.27	6.293%	$143.7825	$143.78	$143.80	$143.80
Purchase #2	$40.41	8.752%	$43.9467	$43.95	$43.95	$43.90
Purchase #3	$51.72	12.247%	$58.0541	$58.05	$58.05	$58.10
Purchase #4	$138.66	9.848%	$152.3152	$152.32	$152.30	$152.30
Purchase #5	$53.50	5.302%	$56.3366	$56.34	$56.35	$56.30
Purchase #6	$62.28	12.456%	$70.0376	$70.04	$70.05	$70.00
Purchase #7	$120.30	9.381%	$131.5853	$131.59	$131.60	$131.60
7 purchase totals =	$602.14		$656.0580	$656.07	$656.10	$656.00