...
4975:.24,
4998:.00,
4999:.00
};

var MSRP = nlapiGetFieldValue('custitem_price_retail');
var SALE = nlapiGetFieldValue('custitem_price_sale');
var INFLATE = "";

if (!SALE) { MSRP = Math.round(MSRP * 10000)/100; INFLATE = PI_array[MSRP]; }
else { SALE = Math.round(SALE * 10000)/100; INFLATE = PI_array[SALE]; }

nlapiSetFieldValue('custitem_item_amzn_price_inflate',INFLATE);