From type/Real

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method round(Real:D: $scale = 1)

Rounds the number to scale $scale. If $scale is 1, rounds to an integer. If scale is 0.1, rounds to one digit after the radix point (period or comma), etc.

From type/Cool

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multi sub round(Numeric(Cool), $scale = 1)
multi method round(Cool:D: $scale = 1)

Coerces the invocant (or in sub form, its argument) to Numeric, and rounds it to the unit of $scale. If $scale is 1, rounds to the nearest integer; an arbitrary scale will result in the closest multiple of that number.

say 1.7.round;          # OUTPUT: «2␤» 
say 1.07.round(0.1);    # OUTPUT: «1.1␤» 
say 21.round(10);       # OUTPUT: «20␤» 
say round(1000, 23.01)  # OUTPUT: «989.43»

Always rounds up if the number is at mid-point:

say (−.5 ).round;       # OUTPUT: «0␤» 
say ( .5 ).round;       # OUTPUT: «1␤» 
say (−.55).round(.1);   # OUTPUT: «-0.5␤» 
say ( .55).round(.1);   # OUTPUT: «0.6␤»

Pay attention to types when using this method, as ending up with the wrong type may affect the precision you seek to achieve. For Numeric types, the type of the result is the type of the argument (Complex argument gets coerced to Numeric, ending up a Num). If rounding a Complex, the result is Complex as well, regardless of the type of the argument.

9930972392403501.round(1)      .raku.say; # OUTPUT: «9930972392403501␤» 
9930972392403501.round(1e0)    .raku.say; # OUTPUT: «9.9309723924035e+15␤» 
9930972392403501.round(1e0).Int.raku.say; # OUTPUT: «9930972392403500␤»

From type/Complex

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multi method round(Complex:D: --> Complex:D)
multi method round(Complex:D: Real() $scale --> Complex:D)

With no arguments, rounds both the real and imaginary parts to the nearest integer and returns a new Complex number. If $scale is given, rounds both parts of the invocant to the nearest multiple of $scale. Uses the same algorithm as Real.round on each part of the number.

say (1.2-3.8i).round;           # OUTPUT: «1-4i␤» 
say (1.256-3.875i).round(0.1);  # OUTPUT: «1.3-3.9i␤»