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	$105.42	10.826%	$116.8328	$116.83	$116.85	$116.80
Purchase #2	$157.57	13.665%	$179.1019	$179.10	$179.10	$179.10
Purchase #3	$188.64	11.572%	$210.4694	$210.47	$210.45	$210.50
Purchase #4	$66.69	13.139%	$75.4524	$75.45	$75.45	$75.50
Purchase #5	$63.59	7.665%	$68.4642	$68.46	$68.45	$68.50
Purchase #6	$23.58	7.758%	$25.4093	$25.41	$25.40	$25.40
Purchase #7	$124.98	13.754%	$142.1697	$142.17	$142.15	$142.20
7 purchase totals =	$730.47		$817.8997	$817.89	$817.85	$818.00