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	$12.92	6.856%	$13.8058	$13.81	$13.80	$13.80
Purchase #2	$114.87	11.319%	$127.8721	$127.87	$127.85	$127.90
Purchase #3	$122.97	8.500%	$133.4225	$133.42	$133.40	$133.40
Purchase #4	$90.76	13.380%	$102.9037	$102.90	$102.90	$102.90
Purchase #5	$57.27	7.739%	$61.7021	$61.70	$61.70	$61.70
Purchase #6	$28.54	10.491%	$31.5341	$31.53	$31.55	$31.50
Purchase #7	$72.77	8.154%	$78.7037	$78.70	$78.70	$78.70
7 purchase totals =	$500.10		$549.9440	$549.93	$549.90	$549.90