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 $129.48   9.387%   $141.6343   $141.63   $141.65   $141.60  
  Purchase #2 $163.94   5.866%   $173.5567   $173.56   $173.55   $173.60  
  Purchase #3 $114.31   6.743%   $122.0179   $122.02   $122.00   $122.00  
  Purchase #4 $76.87   5.644%   $81.2085   $81.21   $81.20   $81.20  
  Purchase #5 $188.39   4.841%   $197.51   $197.51   $197.50   $197.50  
  Purchase #6 $29.68   6.442%   $31.592   $31.59   $31.60   $31.60  
  Purchase #7 $64.73   3.102%   $66.7379   $66.74   $66.75   $66.70  
  7 purchase totals = $767.40       $814.2573   $814.26   $814.25   $814.20