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	$246.48	3.836%	$255.935	$255.94	$255.95	$255.90
Purchase #2	$107.60	11.432%	$119.9008	$119.90	$119.90	$119.90
Purchase #3	$192.52	11.120%	$213.9282	$213.93	$213.95	$213.90
Purchase #4	$39.56	10.291%	$43.6311	$43.63	$43.65	$43.60
Purchase #5	$123.87	11.158%	$137.6914	$137.69	$137.70	$137.70
Purchase #6	$34.60	8.238%	$37.4503	$37.45	$37.45	$37.50
Purchase #7	$175.96	6.609%	$187.5892	$187.59	$187.60	$187.60
7 purchase totals =	$920.59		$996.1260	$996.13	$996.20	$996.10