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	$21.70	8.403%	$23.5235	$23.52	$23.50	$23.50
Purchase #2	$19.80	6.370%	$21.0613	$21.06	$21.05	$21.10
Purchase #3	$130.49	4.807%	$136.7627	$136.76	$136.75	$136.80
Purchase #4	$223.79	11.602%	$249.7541	$249.75	$249.75	$249.80
Purchase #5	$94.92	5.802%	$100.4273	$100.43	$100.45	$100.40
Purchase #6	$81.41	10.241%	$89.7472	$89.75	$89.75	$89.70
Purchase #7	$216.71	11.627%	$241.9069	$241.91	$241.90	$241.90
7 purchase totals =	$788.82		$863.1830	$863.18	$863.15	$863.20