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	$223.25	11.401%	$248.7027	$248.70	$248.70	$248.70
Purchase #2	$41.40	8.536%	$44.9339	$44.93	$44.95	$44.90
Purchase #3	$20.83	4.735%	$21.8163	$21.82	$21.80	$21.80
Purchase #4	$196.49	9.311%	$214.7852	$214.79	$214.80	$214.80
Purchase #5	$76.26	8.781%	$82.9564	$82.96	$82.95	$83.00
Purchase #6	$38.79	5.425%	$40.8944	$40.89	$40.90	$40.90
Purchase #7	$94.76	11.652%	$105.8014	$105.80	$105.80	$105.80
7 purchase totals =	$691.78		$759.8903	$759.89	$759.90	$759.90