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 $119.35   5.672%   $126.1195   $126.12   $126.10   $126.10  
  Purchase #2 $179.55   6.769%   $191.7037   $191.70   $191.70   $191.70  
  Purchase #3 $43.55   8.198%   $47.1202   $47.12   $47.10   $47.10  
  Purchase #4 $205.81   9.154%   $224.6498   $224.65   $224.65   $224.60  
  Purchase #5 $25.37   3.114%   $26.16   $26.16   $26.15   $26.20  
  Purchase #6 $241.65   3.314%   $249.6583   $249.66   $249.65   $249.70  
  Purchase #7 $123.88   11.329%   $137.9144   $137.91   $137.90   $137.90  
  7 purchase totals = $939.16       $1,003.3259   $1,003.32   $1,003.25   $1,003.30