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 $249.87   4.544%   $261.2241   $261.22   $261.20   $261.20  
  Purchase #2 $68.40   7.385%   $73.4513   $73.45   $73.45   $73.50  
  Purchase #3 $188.33   6.664%   $200.8803   $200.88   $200.90   $200.90  
  Purchase #4 $143.89   12.576%   $161.9856   $161.99   $162.00   $162.00  
  Purchase #5 $207.99   6.117%   $220.7127   $220.71   $220.70   $220.70  
  Purchase #6 $62.45   9.430%   $68.339   $68.34   $68.35   $68.30  
  Purchase #7 $33.90   12.290%   $38.0663   $38.07   $38.05   $38.10  
  7 purchase totals = $954.83       $1,024.6593   $1,024.66   $1,024.65   $1,024.70