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	$73.92	6.573%	$78.7788	$78.78	$78.80	$78.80
Purchase #2	$98.88	12.645%	$111.3834	$111.38	$111.40	$111.40
Purchase #3	$116.31	13.468%	$131.9746	$131.97	$131.95	$132.00
Purchase #4	$98.27	7.400%	$105.542	$105.54	$105.55	$105.50
Purchase #5	$190.42	8.442%	$206.4953	$206.50	$206.50	$206.50
Purchase #6	$249.29	3.106%	$257.0329	$257.03	$257.05	$257.00
Purchase #7	$17.87	6.403%	$19.0142	$19.01	$19.00	$19.00
7 purchase totals =	$844.96		$910.2212	$910.21	$910.25	$910.20