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	$80.52	9.759%	$88.3779	$88.38	$88.40	$88.40
Purchase #2	$106.48	3.120%	$109.8022	$109.80	$109.80	$109.80
Purchase #3	$61.77	9.270%	$67.4961	$67.50	$67.50	$67.50
Purchase #4	$196.40	13.491%	$222.8963	$222.90	$222.90	$222.90
Purchase #5	$205.69	9.248%	$224.7122	$224.71	$224.70	$224.70
Purchase #6	$122.70	3.581%	$127.0939	$127.09	$127.10	$127.10
Purchase #7	$17.85	8.584%	$19.3822	$19.38	$19.40	$19.40
7 purchase totals =	$791.41		$859.7608	$859.76	$859.80	$859.80