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 $231.90   13.380%   $262.9282   $262.93   $262.95   $262.90  
  Purchase #2 $228.94   13.282%   $259.3478   $259.35   $259.35   $259.30  
  Purchase #3 $54.34   9.424%   $59.461   $59.46   $59.45   $59.50  
  Purchase #4 $63.40   7.681%   $68.2698   $68.27   $68.25   $68.30  
  Purchase #5 $167.85   13.653%   $190.7666   $190.77   $190.75   $190.80  
  Purchase #6 $154.81   13.696%   $176.0128   $176.01   $176.00   $176.00  
  Purchase #7 $228.85   12.622%   $257.7354   $257.74   $257.75   $257.70  
  7 purchase totals = $1,130.09       $1,274.5216   $1,274.53   $1,274.50   $1,274.50