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 $63.38   6.402%   $67.4376   $67.44   $67.45   $67.40  
  Purchase #2 $231.46   9.188%   $252.7265   $252.73   $252.75   $252.70  
  Purchase #3 $115.25   6.558%   $122.8081   $122.81   $122.80   $122.80  
  Purchase #4 $45.72   6.872%   $48.8619   $48.86   $48.85   $48.90  
  Purchase #5 $190.68   6.217%   $202.5346   $202.53   $202.55   $202.50  
  Purchase #6 $85.36   7.818%   $92.0334   $92.03   $92.05   $92.00  
  Purchase #7 $223.85   11.856%   $250.3897   $250.39   $250.40   $250.40  
  7 purchase totals = $955.70       $1,036.7918   $1,036.79   $1,036.85   $1,036.70