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	$40.95	11.332%	$45.5905	$45.59	$45.60	$45.60
Purchase #2	$42.98	6.858%	$45.9276	$45.93	$45.95	$45.90
Purchase #3	$206.74	9.438%	$226.2521	$226.25	$226.25	$226.30
Purchase #4	$231.89	11.516%	$258.5945	$258.59	$258.60	$258.60
Purchase #5	$107.53	3.243%	$111.0172	$111.02	$111.00	$111.00
Purchase #6	$13.65	5.294%	$14.3726	$14.37	$14.35	$14.40
Purchase #7	$152.63	9.680%	$167.4046	$167.40	$167.40	$167.40
7 purchase totals =	$796.37		$869.1591	$869.15	$869.15	$869.20