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	$108.78	12.570%	$122.4536	$122.45	$122.45	$122.50
Purchase #2	$215.38	8.406%	$233.4848	$233.48	$233.50	$233.50
Purchase #3	$102.55	8.632%	$111.4021	$111.40	$111.40	$111.40
Purchase #4	$164.43	3.629%	$170.3972	$170.40	$170.40	$170.40
Purchase #5	$183.34	8.181%	$198.339	$198.34	$198.35	$198.30
Purchase #6	$27.93	10.576%	$30.8839	$30.88	$30.90	$30.90
Purchase #7	$12.50	3.142%	$12.8928	$12.89	$12.90	$12.90
7 purchase totals =	$814.91		$879.8534	$879.84	$879.90	$879.90