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 $200.51   5.151%   $210.8383   $210.84   $210.85   $210.80  
  Purchase #2 $213.87   8.408%   $231.8522   $231.85   $231.85   $231.90  
  Purchase #3 $52.48   8.697%   $57.0442   $57.04   $57.05   $57.00  
  Purchase #4 $60.92   7.404%   $65.4305   $65.43   $65.45   $65.40  
  Purchase #5 $134.73   8.868%   $146.6779   $146.68   $146.70   $146.70  
  Purchase #6 $26.72   6.346%   $28.4157   $28.42   $28.40   $28.40  
  Purchase #7 $49.78   8.786%   $54.1537   $54.15   $54.15   $54.20  
  7 purchase totals = $739.01       $794.4125   $794.41   $794.45   $794.40