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 $23.90   13.226%   $27.061   $27.06   $27.05   $27.10  
  Purchase #2 $90.49   3.514%   $93.6698   $93.67   $93.65   $93.70  
  Purchase #3 $26.36   9.418%   $28.8426   $28.84   $28.85   $28.80  
  Purchase #4 $250.46   10.375%   $276.4452   $276.45   $276.45   $276.40  
  Purchase #5 $224.86   9.688%   $246.6444   $246.64   $246.65   $246.60  
  Purchase #6 $201.54   8.125%   $217.9151   $217.92   $217.90   $217.90  
  Purchase #7 $111.89   12.432%   $125.8002   $125.80   $125.80   $125.80  
  7 purchase totals = $929.50       $1,016.3783   $1,016.38   $1,016.35   $1,016.30