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 $23.68   13.777%   $26.9424   $26.94   $26.95   $26.90  
  Purchase #2 $56.72   9.177%   $61.9252   $61.93   $61.95   $61.90  
  Purchase #3 $213.68   11.857%   $239.016   $239.02   $239.00   $239.00  
  Purchase #4 $71.77   9.872%   $78.8551   $78.86   $78.85   $78.90  
  Purchase #5 $207.35   7.338%   $222.5653   $222.57   $222.55   $222.60  
  Purchase #6 $9.53   4.585%   $9.967   $9.97   $9.95   $10.00  
  Purchase #7 $224.39   3.213%   $231.5997   $231.60   $231.60   $231.60  
  7 purchase totals = $807.12       $870.8707   $870.89   $870.85   $870.90