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 $49.28   11.723%   $55.0571   $55.06   $55.05   $55.10  
  Purchase #2 $230.27   13.745%   $261.9206   $261.92   $261.90   $261.90  
  Purchase #3 $35.89   5.725%   $37.9447   $37.94   $37.95   $37.90  
  Purchase #4 $71.51   8.870%   $77.8529   $77.85   $77.85   $77.90  
  Purchase #5 $224.75   8.602%   $244.083   $244.08   $244.10   $244.10  
  Purchase #6 $150.53   7.292%   $161.5066   $161.51   $161.50   $161.50  
  Purchase #7 $25.29   13.142%   $28.6136   $28.61   $28.60   $28.60  
  7 purchase totals = $787.52       $866.9785   $866.97   $866.95   $867.00