Helper functions to round screen coordinates and dimensions to screen scale.

gistfile1.m

CGFloat CGFloatAdjustToScreenScale(CGFloat value, NSRoundingMode mode) {
    CGFloat (*roundingFunction)(CGFloat);
    switch (mode) {
        case NSRoundPlain:  roundingFunction = &roundf; break;
        case NSRoundUp:     roundingFunction = &ceilf; break;
        case NSRoundDown:   roundingFunction = &floorf; break;
        case NSRoundBankers:roundingFunction = &roundf; break;
    }
    CGFloat scale = [[UIScreen mainScreen] scale];
    CGFloat result = roundingFunction(value * scale) / scale;
    return result;
}

CGPoint CGPointAdjustToScreenScale(CGPoint point, NSRoundingMode mode) {
    return CGPointMake(CGFloatAdjustToScreenScale(point.x, mode),
                       CGFloatAdjustToScreenScale(point.y, mode));
}

CGSize CGSizeAdjustToScreenScale(CGSize size, NSRoundingMode mode) {
    return CGSizeMake(CGFloatAdjustToScreenScale(size.width, mode),
                      CGFloatAdjustToScreenScale(size.height, mode));
}

CGRect CGRectAdjustToScreenScale(CGRect rect, NSRoundingMode mode) {
    return CGRectMake(CGFloatAdjustToScreenScale(rect.origin.x, mode),
                      CGFloatAdjustToScreenScale(rect.origin.y, mode),
                      CGFloatAdjustToScreenScale(rect.size.width, mode),
                      CGFloatAdjustToScreenScale(rect.size.height, mode));
}

gistfile2.m

// Example
CGFloat value = 3.61;

// On non-Retina screens with scale 1:
CGFloat nonRetina = CGFloatAdjustToScreenScale( value, NSRoundPlain );
// nonRetina is equal to 4

// On Retina screens with scale 2:
CGFloat retina = CGFloatAdjustToScreenScale( value, NSRoundPlain );
// retina is equal to 3.5


// Use different values for rounding mode, based on what you want to achieve.
// NSRoundUp is good for fitting sizes, because it will never return smaller values.