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	$46.86	12.182%	$52.5685	$52.57	$52.55	$52.60
Purchase #2	$141.50	10.389%	$156.2004	$156.20	$156.20	$156.20
Purchase #3	$123.47	3.297%	$127.5408	$127.54	$127.55	$127.50
Purchase #4	$202.56	4.789%	$212.2606	$212.26	$212.25	$212.30
Purchase #5	$124.70	5.476%	$131.5286	$131.53	$131.55	$131.50
Purchase #6	$19.32	9.390%	$21.1341	$21.13	$21.15	$21.10
Purchase #7	$204.38	5.783%	$216.1993	$216.20	$216.20	$216.20
7 purchase totals =	$862.79		$917.4323	$917.43	$917.45	$917.40