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	$75.98	9.807%	$83.4314	$83.43	$83.45	$83.40
Purchase #2	$121.27	5.518%	$127.9617	$127.96	$127.95	$128.00
Purchase #3	$73.82	12.490%	$83.0401	$83.04	$83.05	$83.00
Purchase #4	$45.53	13.413%	$51.6369	$51.64	$51.65	$51.60
Purchase #5	$63.91	4.174%	$66.5776	$66.58	$66.60	$66.60
Purchase #6	$8.70	13.720%	$9.8936	$9.89	$9.90	$9.90
Purchase #7	$63.98	6.142%	$67.9097	$67.91	$67.90	$67.90
7 purchase totals =	$453.19		$490.4510	$490.45	$490.50	$490.40