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	$5.67	12.664%	$6.388	$6.39	$6.40	$6.40
Purchase #2	$183.42	9.247%	$200.3808	$200.38	$200.40	$200.40
Purchase #3	$114.81	8.238%	$124.268	$124.27	$124.25	$124.30
Purchase #4	$37.91	13.527%	$43.0381	$43.04	$43.05	$43.00
Purchase #5	$243.94	8.420%	$264.4797	$264.48	$264.50	$264.50
Purchase #6	$89.37	9.237%	$97.6251	$97.63	$97.65	$97.60
Purchase #7	$185.31	13.641%	$210.5881	$210.59	$210.60	$210.60
7 purchase totals =	$860.43		$946.7678	$946.78	$946.85	$946.80