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 $54.62   5.629%   $57.6946   $57.69   $57.70   $57.70  
  Purchase #2 $52.76   3.121%   $54.4066   $54.41   $54.40   $54.40  
  Purchase #3 $146.48   5.596%   $154.677   $154.68   $154.70   $154.70  
  Purchase #4 $173.90   8.723%   $189.0693   $189.07   $189.05   $189.10  
  Purchase #5 $235.44   12.367%   $264.5569   $264.56   $264.55   $264.60  
  Purchase #6 $212.30   3.306%   $219.3186   $219.32   $219.30   $219.30  
  Purchase #7 $247.77   5.449%   $261.271   $261.27   $261.25   $261.30  
  7 purchase totals = $1,123.27       $1,200.9940   $1,201.00   $1,200.95   $1,201.10