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	$49.51	8.678%	$53.8065	$53.81	$53.80	$53.80
Purchase #2	$143.85	12.735%	$162.1693	$162.17	$162.15	$162.20
Purchase #3	$83.97	7.191%	$90.0083	$90.01	$90.00	$90.00
Purchase #4	$62.93	10.706%	$69.6673	$69.67	$69.65	$69.70
Purchase #5	$28.91	10.249%	$31.873	$31.87	$31.85	$31.90
Purchase #6	$108.29	5.792%	$114.5622	$114.56	$114.55	$114.60
Purchase #7	$63.34	6.182%	$67.2557	$67.26	$67.25	$67.30
7 purchase totals =	$540.80		$589.3423	$589.35	$589.25	$589.50