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	$12.54	10.654%	$13.876	$13.88	$13.90	$13.90
Purchase #2	$199.66	4.345%	$208.3352	$208.34	$208.35	$208.30
Purchase #3	$127.92	10.831%	$141.775	$141.78	$141.80	$141.80
Purchase #4	$127.96	6.751%	$136.5986	$136.60	$136.60	$136.60
Purchase #5	$71.61	9.118%	$78.1394	$78.14	$78.15	$78.10
Purchase #6	$177.61	6.746%	$189.5916	$189.59	$189.60	$189.60
Purchase #7	$194.63	8.182%	$210.5546	$210.55	$210.55	$210.60
7 purchase totals =	$911.93		$978.8704	$978.88	$978.95	$978.90