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 $37.99   7.169%   $40.7135   $40.71   $40.70   $40.70  
  Purchase #2 $107.76   13.765%   $122.5932   $122.59   $122.60   $122.60  
  Purchase #3 $174.78   9.814%   $191.9329   $191.93   $191.95   $191.90  
  Purchase #4 $69.28   9.786%   $76.0597   $76.06   $76.05   $76.10  
  Purchase #5 $19.88   8.311%   $21.5322   $21.53   $21.55   $21.50  
  Purchase #6 $126.76   8.399%   $137.4066   $137.41   $137.40   $137.40  
  Purchase #7 $125.53   10.489%   $138.6968   $138.70   $138.70   $138.70  
  7 purchase totals = $661.98       $728.9349   $728.93   $728.95   $728.90