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 $24.45   9.341%   $26.7339   $26.73   $26.75   $26.70  
  Purchase #2 $86.69   6.823%   $92.6049   $92.60   $92.60   $92.60  
  Purchase #3 $224.38   12.629%   $252.717   $252.72   $252.70   $252.70  
  Purchase #4 $217.46   5.814%   $230.1031   $230.10   $230.10   $230.10  
  Purchase #5 $227.31   3.836%   $236.0296   $236.03   $236.05   $236.00  
  Purchase #6 $135.54   3.782%   $140.6661   $140.67   $140.65   $140.70  
  Purchase #7 $240.67   5.744%   $254.4941   $254.49   $254.50   $254.50  
  7 purchase totals = $1,156.50       $1,233.3487   $1,233.34   $1,233.35   $1,233.30