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 $49.94   10.524%   $55.1957   $55.20   $55.20   $55.20  
  Purchase #2 $227.38   11.597%   $253.7493   $253.75   $253.75   $253.70  
  Purchase #3 $217.45   6.421%   $231.4125   $231.41   $231.40   $231.40  
  Purchase #4 $8.76   11.163%   $9.7379   $9.74   $9.75   $9.70  
  Purchase #5 $54.89   4.488%   $57.3535   $57.35   $57.35   $57.40  
  Purchase #6 $179.28   12.522%   $201.7294   $201.73   $201.75   $201.70  
  Purchase #7 $203.71   5.810%   $215.5456   $215.55   $215.55   $215.50  
  7 purchase totals = $941.41       $1,024.7239   $1,024.73   $1,024.75   $1,024.60