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	$70.41	10.590%	$77.8664	$77.87	$77.85	$77.90
Purchase #2	$34.50	5.635%	$36.4441	$36.44	$36.45	$36.40
Purchase #3	$196.50	4.581%	$205.5017	$205.50	$205.50	$205.50
Purchase #4	$234.61	6.778%	$250.5119	$250.51	$250.50	$250.50
Purchase #5	$18.98	12.696%	$21.3897	$21.39	$21.40	$21.40
Purchase #6	$78.28	3.386%	$80.9306	$80.93	$80.95	$80.90
Purchase #7	$196.96	9.874%	$216.4078	$216.41	$216.40	$216.40
7 purchase totals =	$830.24		$889.0522	$889.05	$889.05	$889.00