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	$122.85	10.699%	$135.9937	$135.99	$136.00	$136.00
Purchase #2	$48.27	13.869%	$54.9646	$54.96	$54.95	$55.00
Purchase #3	$37.59	4.829%	$39.4052	$39.41	$39.40	$39.40
Purchase #4	$117.86	4.594%	$123.2745	$123.27	$123.25	$123.30
Purchase #5	$125.33	9.372%	$137.0759	$137.08	$137.10	$137.10
Purchase #6	$113.37	12.680%	$127.7453	$127.75	$127.75	$127.70
Purchase #7	$40.81	6.547%	$43.4818	$43.48	$43.50	$43.50
7 purchase totals =	$606.08		$661.9410	$661.94	$661.95	$662.00