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	$34.35	11.681%	$38.3624	$38.36	$38.35	$38.40
Purchase #2	$193.59	3.585%	$200.5302	$200.53	$200.55	$200.50
Purchase #3	$154.64	6.638%	$164.905	$164.91	$164.90	$164.90
Purchase #4	$51.75	4.543%	$54.101	$54.10	$54.10	$54.10
Purchase #5	$127.82	10.172%	$140.8219	$140.82	$140.80	$140.80
Purchase #6	$179.27	13.684%	$203.8013	$203.80	$203.80	$203.80
Purchase #7	$128.52	7.352%	$137.9688	$137.97	$137.95	$138.00
7 purchase totals =	$869.94		$940.4906	$940.49	$940.45	$940.50