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 $24.72   5.845%   $26.1649   $26.16   $26.15   $26.20  
  Purchase #2 $228.93   3.356%   $236.6129   $236.61   $236.60   $236.60  
  Purchase #3 $98.95   11.632%   $110.4599   $110.46   $110.45   $110.50  
  Purchase #4 $114.73   4.860%   $120.3059   $120.31   $120.30   $120.30  
  Purchase #5 $76.34   3.416%   $78.9478   $78.95   $78.95   $78.90  
  Purchase #6 $204.74   8.746%   $222.6466   $222.65   $222.65   $222.60  
  Purchase #7 $179.40   12.583%   $201.9739   $201.97   $201.95   $202.00  
  7 purchase totals = $927.81       $997.1119   $997.11   $997.05   $997.10