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 $231.98   13.455%   $263.1929   $263.19   $263.20   $263.20  
  Purchase #2 $228.87   6.792%   $244.4149   $244.41   $244.40   $244.40  
  Purchase #3 $247.66   13.298%   $280.5938   $280.59   $280.60   $280.60  
  Purchase #4 $24.73   10.554%   $27.34   $27.34   $27.35   $27.30  
  Purchase #5 $233.73   11.104%   $259.6834   $259.68   $259.70   $259.70  
  Purchase #6 $147.60   6.780%   $157.6073   $157.61   $157.60   $157.60  
  Purchase #7 $232.99   12.492%   $262.0951   $262.10   $262.10   $262.10  
  7 purchase totals = $1,347.56       $1,494.9274   $1,494.92   $1,494.95   $1,494.90