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 $193.59   7.514%   $208.1364   $208.14   $208.15   $208.10  
  Purchase #2 $118.79   5.365%   $125.1631   $125.16   $125.15   $125.20  
  Purchase #3 $41.34   3.115%   $42.6277   $42.63   $42.65   $42.60  
  Purchase #4 $163.56   7.266%   $175.4443   $175.44   $175.45   $175.40  
  Purchase #5 $215.66   13.847%   $245.5224   $245.52   $245.50   $245.50  
  Purchase #6 $52.39   12.380%   $58.8759   $58.88   $58.90   $58.90  
  Purchase #7 $199.83   5.423%   $210.6668   $210.67   $210.65   $210.70  
  7 purchase totals = $985.16       $1,066.4366   $1,066.44   $1,066.45   $1,066.40