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 $98.41   6.259%   $104.5695   $104.57   $104.55   $104.60  
  Purchase #2 $49.67   6.299%   $52.7987   $52.80   $52.80   $52.80  
  Purchase #3 $36.45   12.284%   $40.9275   $40.93   $40.95   $40.90  
  Purchase #4 $28.41   5.693%   $30.0274   $30.03   $30.05   $30.00  
  Purchase #5 $55.71   8.735%   $60.5763   $60.58   $60.60   $60.60  
  Purchase #6 $51.72   8.627%   $56.1819   $56.18   $56.20   $56.20  
  Purchase #7 $250.81   12.798%   $282.9087   $282.91   $282.90   $282.90  
  7 purchase totals = $571.18       $627.9900   $628.00   $628.05   $628.00