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 $42.72   13.778%   $48.606   $48.61   $48.60   $48.60  
  Purchase #2 $234.71   6.476%   $249.9098   $249.91   $249.90   $249.90  
  Purchase #3 $59.84   6.410%   $63.6757   $63.68   $63.70   $63.70  
  Purchase #4 $149.71   5.295%   $157.6371   $157.64   $157.65   $157.60  
  Purchase #5 $78.86   3.564%   $81.6706   $81.67   $81.65   $81.70  
  Purchase #6 $125.55   13.131%   $142.036   $142.04   $142.05   $142.00  
  Purchase #7 $62.71   6.243%   $66.625   $66.63   $66.65   $66.60  
  7 purchase totals = $754.10       $810.1602   $810.18   $810.20   $810.10