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	$172.93	3.838%	$179.5671	$179.57	$179.55	$179.60
Purchase #2	$145.68	10.459%	$160.9167	$160.92	$160.90	$160.90
Purchase #3	$104.81	12.510%	$117.9217	$117.92	$117.90	$117.90
Purchase #4	$75.72	8.409%	$82.0873	$82.09	$82.10	$82.10
Purchase #5	$49.51	4.679%	$51.8266	$51.83	$51.85	$51.80
Purchase #6	$25.50	13.445%	$28.9285	$28.93	$28.95	$28.90
Purchase #7	$38.34	6.853%	$40.9674	$40.97	$40.95	$41.00
7 purchase totals =	$612.49		$662.2153	$662.23	$662.20	$662.20