It has been shown that under perfect competition and a Cobb-Douglas production function, a basic real business cycle model may exhibit indeterminacy and sunspots fluctuations when income tax rates are determined by a balanced-budget rule. This paper introduces in an otherwise standard real business cycle model a more general and data coherent class of production functions, namely a constant elasticity of substitution production function. We show that the degree of substitutability between production factors is a key ingredient to understand the (de)stabilising properties of a balanced-budget rule. Furthermore, when we calibrate the model consistently with the empirical evidence, i.e. the elasticity of substitutions between labour and capital below unity, balanced-budget rules deliver determinacy for a broad range of OECD countries.