这个是系统方法

- (NSString*)Rounding:(float)number afterPoint:(NSInteger)position{     NSDecimalNumberHandler *handler = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode: NSRoundPlain scale: position raiseOnExactness: NO raiseOnOverflow: NO raiseOnUnderflow:YES raiseOnDivideByZero: NO];     NSDecimalNumber *floatDecimal = [[NSDecimalNumber alloc] initWithFloat: number];     NSDecimalNumber *resultNumber = [floatDecimal decimalNumberByRoundingAccordingToBehavior:handler];     return [NSString stringWithFormat:@"%@",resultNumber];}

我用的是下面这个方法，注意⚠️只有在保留4位以下小数时四舍五入才正常

- (NSString*)Rounding:(double)number afterPoint:(NSInteger)position{    NSNumber *priceNum = [NSNumber numberWithDouble:number];    NSString *string = [NSString stringWithFormat:@"%.10f",number];    NSRange range = [string rangeOfString:@"."];    if (range.location!=NSNotFound) {                NSInteger loc = range.location+position+1;        NSRange rangeS;        if (string.length>loc) {            rangeS = NSMakeRange(loc, 1);            NSString *str = [string substringWithRange:rangeS];            if (str!=nil&&[str floatValue]>=5.0f) {                priceNum = [NSNumber numberWithDouble:[[string stringByReplacingCharactersInRange:rangeS withString:@"9"] floatValue]];            }        }            }    if (position>4) {        return @"";    }        if (position==1) {//保留1位        return [NSString stringWithFormat:@"%.1f",round([priceNum floatValue]*1000000000000)/1000000000000];    }else if(position==2){//保留2位        return [NSString stringWithFormat:@"%.2f",round([priceNum floatValue]*1000000000000)/1000000000000];    }else if(position==3){//保留3位        return [NSString stringWithFormat:@"%.3f",round([priceNum floatValue]*1000000000000)/1000000000000];    }else if(position==4){//保留4位        return [NSString stringWithFormat:@"%.4f",round([priceNum floatValue]*1000000000000)/1000000000000];    }        //默认保留2位    return [NSString stringWithFormat:@"%.2f",round([priceNum floatValue]*1000000000000)/1000000000000];}

使用方法：

//保留小数点后2位，因为第3位小数大于5，所以第2位进1[self Rounding:100.11545  afterPoint:2]//结果返回 100.12//保留小数点后4位，因为第5位小数大于5，所以第4位进1[self Rounding: 100.11545  afterPoint:4]//100.1155//保留小数点后3位，因为第4位小数小于5，所以舍去[self Rounding: 100.11545  afterPoint:3]//100.115