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	$247.43	3.824%	$256.8917	$256.89	$256.90	$256.90
Purchase #2	$40.63	6.694%	$43.3498	$43.35	$43.35	$43.30
Purchase #3	$12.78	6.620%	$13.626	$13.63	$13.65	$13.60
Purchase #4	$196.42	12.831%	$221.6227	$221.62	$221.60	$221.60
Purchase #5	$83.87	7.386%	$90.0646	$90.06	$90.05	$90.10
Purchase #6	$49.88	9.746%	$54.7413	$54.74	$54.75	$54.70
Purchase #7	$32.76	8.314%	$35.4837	$35.48	$35.50	$35.50
7 purchase totals =	$663.77		$715.7798	$715.77	$715.80	$715.70