Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $206.57   4.370%   $215.5971   $215.60   $215.60   $215.60  
  Purchase #2 $14.56   10.635%   $16.1085   $16.11   $16.10   $16.10  
  Purchase #3 $59.47   3.591%   $61.6056   $61.61   $61.60   $61.60  
  Purchase #4 $122.43   9.584%   $134.1637   $134.16   $134.15   $134.20  
  Purchase #5 $100.38   11.647%   $112.0713   $112.07   $112.05   $112.10  
  Purchase #6 $235.48   9.710%   $258.3451   $258.35   $258.35   $258.30  
  Purchase #7 $221.77   5.379%   $233.699   $233.70   $233.70   $233.70  
  7 purchase totals = $960.66       $1,031.5903   $1,031.60   $1,031.55   $1,031.60