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	$73.46	13.606%	$83.455	$83.46	$83.45	$83.50
Purchase #2	$74.48	9.439%	$81.5102	$81.51	$81.50	$81.50
Purchase #3	$239.89	12.705%	$270.368	$270.37	$270.35	$270.40
Purchase #4	$184.61	7.177%	$197.8595	$197.86	$197.85	$197.90
Purchase #5	$7.77	10.441%	$8.5813	$8.58	$8.60	$8.60
Purchase #6	$77.27	6.378%	$82.1983	$82.20	$82.20	$82.20
Purchase #7	$213.94	11.492%	$238.526	$238.53	$238.55	$238.50
7 purchase totals =	$871.42		$962.4983	$962.51	$962.50	$962.60