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	$127.46	12.568%	$143.4792	$143.48	$143.50	$143.50
Purchase #2	$249.97	9.798%	$274.4621	$274.46	$274.45	$274.50
Purchase #3	$230.31	13.219%	$260.7547	$260.75	$260.75	$260.80
Purchase #4	$215.35	5.837%	$227.92	$227.92	$227.90	$227.90
Purchase #5	$75.79	8.844%	$82.4929	$82.49	$82.50	$82.50
Purchase #6	$15.28	12.214%	$17.1463	$17.15	$17.15	$17.10
Purchase #7	$155.61	10.674%	$172.2198	$172.22	$172.20	$172.20
7 purchase totals =	$1,069.77		$1,178.4750	$1,178.47	$1,178.45	$1,178.50