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 $202.74   12.334%   $227.746   $227.75   $227.75   $227.70  
  Purchase #2 $31.52   5.574%   $33.2769   $33.28   $33.30   $33.30  
  Purchase #3 $60.97   8.837%   $66.3579   $66.36   $66.35   $66.40  
  Purchase #4 $124.32   9.500%   $136.1304   $136.13   $136.15   $136.10  
  Purchase #5 $154.95   6.407%   $164.8776   $164.88   $164.90   $164.90  
  Purchase #6 $24.74   5.564%   $26.1165   $26.12   $26.10   $26.10  
  Purchase #7 $126.73   10.574%   $140.1304   $140.13   $140.15   $140.10  
  7 purchase totals = $725.97       $794.6357   $794.65   $794.70   $794.60