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	$75.60	7.746%	$81.456	$81.46	$81.45	$81.50
Purchase #2	$231.32	12.636%	$260.5496	$260.55	$260.55	$260.50
Purchase #3	$78.82	13.146%	$89.1817	$89.18	$89.20	$89.20
Purchase #4	$216.56	10.590%	$239.4937	$239.49	$239.50	$239.50
Purchase #5	$90.85	11.681%	$101.4622	$101.46	$101.45	$101.50
Purchase #6	$82.45	6.659%	$87.9403	$87.94	$87.95	$87.90
Purchase #7	$10.63	10.378%	$11.7332	$11.73	$11.75	$11.70
7 purchase totals =	$786.23		$871.8167	$871.81	$871.85	$871.80