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 $85.83   9.782%   $94.2259   $94.23   $94.25   $94.20  
  Purchase #2 $62.43   8.461%   $67.7122   $67.71   $67.70   $67.70  
  Purchase #3 $242.86   9.223%   $265.259   $265.26   $265.25   $265.30  
  Purchase #4 $149.97   7.751%   $161.5942   $161.59   $161.60   $161.60  
  Purchase #5 $66.90   9.558%   $73.2943   $73.29   $73.30   $73.30  
  Purchase #6 $122.71   12.465%   $138.0058   $138.01   $138.00   $138.00  
  Purchase #7 $47.50   10.326%   $52.4049   $52.40   $52.40   $52.40  
  7 purchase totals = $778.20       $852.4963   $852.49   $852.50   $852.50