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	$20.82	4.297%	$21.7146	$21.71	$21.70	$21.70
Purchase #2	$149.77	11.158%	$166.4813	$166.48	$166.50	$166.50
Purchase #3	$37.93	12.670%	$42.7357	$42.74	$42.75	$42.70
Purchase #4	$83.28	5.520%	$87.8771	$87.88	$87.90	$87.90
Purchase #5	$214.34	8.182%	$231.8773	$231.88	$231.90	$231.90
Purchase #6	$87.45	7.399%	$93.9204	$93.92	$93.90	$93.90
Purchase #7	$212.97	4.243%	$222.0063	$222.01	$222.00	$222.00
7 purchase totals =	$806.56		$866.6127	$866.62	$866.65	$866.60