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 $59.89   13.437%   $67.9374   $67.94   $67.95   $67.90  
  Purchase #2 $245.53   4.642%   $256.9275   $256.93   $256.95   $256.90  
  Purchase #3 $161.76   11.293%   $180.0276   $180.03   $180.05   $180.00  
  Purchase #4 $30.98   8.475%   $33.6056   $33.61   $33.60   $33.60  
  Purchase #5 $178.85   10.750%   $198.0764   $198.08   $198.10   $198.10  
  Purchase #6 $126.36   13.176%   $143.0092   $143.01   $143.00   $143.00  
  Purchase #7 $15.95   8.824%   $17.3574   $17.36   $17.35   $17.40  
  7 purchase totals = $819.32       $896.9411   $896.96   $897.00   $896.90