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 $245.77   9.632%   $269.4426   $269.44   $269.45   $269.40  
  Purchase #2 $232.59   3.645%   $241.0679   $241.07   $241.05   $241.10  
  Purchase #3 $67.56   6.465%   $71.9278   $71.93   $71.95   $71.90  
  Purchase #4 $22.70   9.339%   $24.82   $24.82   $24.80   $24.80  
  Purchase #5 $47.87   8.176%   $51.7839   $51.78   $51.80   $51.80  
  Purchase #6 $240.55   9.254%   $262.8105   $262.81   $262.80   $262.80  
  Purchase #7 $78.44   4.248%   $81.7721   $81.77   $81.75   $81.80  
  7 purchase totals = $935.48       $1,003.6248   $1,003.62   $1,003.60   $1,003.60