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 $72.71   8.315%   $78.7558   $78.76   $78.75   $78.80  
  Purchase #2 $59.56   5.243%   $62.6827   $62.68   $62.70   $62.70  
  Purchase #3 $209.99   11.397%   $233.9226   $233.92   $233.90   $233.90  
  Purchase #4 $225.47   10.636%   $249.451   $249.45   $249.45   $249.50  
  Purchase #5 $232.46   11.193%   $258.4792   $258.48   $258.50   $258.50  
  Purchase #6 $15.62   3.801%   $16.2137   $16.21   $16.20   $16.20  
  Purchase #7 $115.28   9.227%   $125.9169   $125.92   $125.90   $125.90  
  7 purchase totals = $931.09       $1,025.4219   $1,025.42   $1,025.40   $1,025.50