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	$39.93	8.361%	$43.2685	$43.27	$43.25	$43.30
Purchase #2	$102.83	8.192%	$111.2538	$111.25	$111.25	$111.30
Purchase #3	$208.67	6.573%	$222.3859	$222.39	$222.40	$222.40
Purchase #4	$182.62	10.870%	$202.4708	$202.47	$202.45	$202.50
Purchase #5	$71.91	4.219%	$74.9439	$74.94	$74.95	$74.90
Purchase #6	$43.92	4.233%	$45.7791	$45.78	$45.80	$45.80
Purchase #7	$221.72	7.719%	$238.8346	$238.83	$238.85	$238.80
7 purchase totals =	$871.60		$938.9366	$938.93	$938.95	$939.00