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	$82.70	3.284%	$85.4159	$85.42	$85.40	$85.40
Purchase #2	$35.93	7.162%	$38.5033	$38.50	$38.50	$38.50
Purchase #3	$92.76	8.611%	$100.7476	$100.75	$100.75	$100.70
Purchase #4	$237.73	8.716%	$258.4505	$258.45	$258.45	$258.50
Purchase #5	$140.93	5.281%	$148.3725	$148.37	$148.35	$148.40
Purchase #6	$246.99	11.540%	$275.4926	$275.49	$275.50	$275.50
Purchase #7	$137.71	8.322%	$149.1702	$149.17	$149.15	$149.20
7 purchase totals =	$974.75		$1,056.1526	$1,056.15	$1,056.10	$1,056.20