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	$5.50	8.153%	$5.9484	$5.95	$5.95	$5.90
Purchase #2	$139.75	10.597%	$154.5593	$154.56	$154.55	$154.60
Purchase #3	$248.84	3.232%	$256.8825	$256.88	$256.90	$256.90
Purchase #4	$93.39	12.853%	$105.3934	$105.39	$105.40	$105.40
Purchase #5	$127.35	13.427%	$144.4493	$144.45	$144.45	$144.40
Purchase #6	$73.91	12.756%	$83.338	$83.34	$83.35	$83.30
Purchase #7	$161.67	3.613%	$167.5111	$167.51	$167.50	$167.50
7 purchase totals =	$850.41		$918.0820	$918.08	$918.10	$918.00