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	$6.83	3.184%	$7.0475	$7.05	$7.05	$7.00
Purchase #2	$128.45	12.420%	$144.4035	$144.40	$144.40	$144.40
Purchase #3	$97.49	3.160%	$100.5707	$100.57	$100.55	$100.60
Purchase #4	$112.86	9.119%	$123.1517	$123.15	$123.15	$123.20
Purchase #5	$82.71	9.656%	$90.6965	$90.70	$90.70	$90.70
Purchase #6	$35.42	8.122%	$38.2968	$38.30	$38.30	$38.30
Purchase #7	$14.36	4.835%	$15.0543	$15.05	$15.05	$15.10
7 purchase totals =	$478.12		$519.2210	$519.22	$519.20	$519.30