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 $196.84   3.553%   $203.8337   $203.83   $203.85   $203.80  
  Purchase #2 $53.46   11.605%   $59.664   $59.66   $59.65   $59.70  
  Purchase #3 $236.66   6.229%   $251.4016   $251.40   $251.40   $251.40  
  Purchase #4 $143.35   13.506%   $162.7109   $162.71   $162.70   $162.70  
  Purchase #5 $125.48   8.341%   $135.9463   $135.95   $135.95   $135.90  
  Purchase #6 $215.55   4.790%   $225.8748   $225.87   $225.85   $225.90  
  Purchase #7 $28.42   6.300%   $30.2105   $30.21   $30.20   $30.20  
  7 purchase totals = $999.76       $1,069.6418   $1,069.63   $1,069.60   $1,069.60