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	$34.70	8.293%	$37.5777	$37.58	$37.60	$37.60
Purchase #2	$136.52	12.720%	$153.8853	$153.89	$153.90	$153.90
Purchase #3	$54.36	10.180%	$59.8938	$59.89	$59.90	$59.90
Purchase #4	$66.99	5.868%	$70.921	$70.92	$70.90	$70.90
Purchase #5	$216.64	13.571%	$246.0402	$246.04	$246.05	$246.00
Purchase #6	$71.82	11.149%	$79.8272	$79.83	$79.85	$79.80
Purchase #7	$121.25	6.244%	$128.8209	$128.82	$128.80	$128.80
7 purchase totals =	$702.28		$776.9661	$776.97	$777.00	$776.90