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	$13.79	13.169%	$15.606	$15.61	$15.60	$15.60
Purchase #2	$201.82	12.861%	$227.7761	$227.78	$227.80	$227.80
Purchase #3	$196.39	6.174%	$208.5151	$208.52	$208.50	$208.50
Purchase #4	$51.86	4.672%	$54.2829	$54.28	$54.30	$54.30
Purchase #5	$152.31	7.794%	$164.181	$164.18	$164.20	$164.20
Purchase #6	$56.47	3.659%	$58.5362	$58.54	$58.55	$58.50
Purchase #7	$140.70	7.680%	$151.5058	$151.51	$151.50	$151.50
7 purchase totals =	$813.34		$880.4031	$880.42	$880.45	$880.40