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	$75.64	9.579%	$82.8856	$82.89	$82.90	$82.90
Purchase #2	$64.46	5.705%	$68.1374	$68.14	$68.15	$68.10
Purchase #3	$215.25	10.111%	$237.0139	$237.01	$237.00	$237.00
Purchase #4	$96.93	3.426%	$100.2508	$100.25	$100.25	$100.30
Purchase #5	$126.61	13.734%	$143.9986	$144.00	$144.00	$144.00
Purchase #6	$132.74	4.220%	$138.3416	$138.34	$138.35	$138.30
Purchase #7	$31.92	9.317%	$34.894	$34.89	$34.90	$34.90
7 purchase totals =	$743.55		$805.5219	$805.52	$805.55	$805.50