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	$50.42	8.824%	$54.8691	$54.87	$54.85	$54.90
Purchase #2	$117.84	3.538%	$122.0092	$122.01	$122.00	$122.00
Purchase #3	$9.36	10.420%	$10.3353	$10.34	$10.35	$10.30
Purchase #4	$124.64	12.234%	$139.8885	$139.89	$139.90	$139.90
Purchase #5	$212.64	7.615%	$228.8325	$228.83	$228.85	$228.80
Purchase #6	$37.32	3.350%	$38.5702	$38.57	$38.55	$38.60
Purchase #7	$68.34	5.570%	$72.1465	$72.15	$72.15	$72.10
7 purchase totals =	$620.56		$666.6513	$666.66	$666.65	$666.60