Every market has a granularity floor: one contract, one micro-lot, one share, or a minimum order value. When your calculated size falls below that floor, the honest answer is to skip the trade, not to round up.
Example: a $6,000 account with a 1% rule has $60 of dollar-risk. A crude oil future with a 40-tick stop risks $400 per contract even in micro-futures form at $40. Taking "just one" turns a 1% rule into a 6.7% rule, and six such trades in a row is a third of the account.
Granularity also shapes which markets suit a small account. Fractional shares, micro futures and small FX lots exist precisely so that sizing stays continuous; without them, a small account is forced into concentration it cannot afford.
Related: position-size-rounding, share-sizing-formula, risk-per-trade, micro-futures