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 $119.34   12.593%   $134.3685   $134.37   $134.35   $134.40  
  Purchase #2 $37.73   3.181%   $38.9302   $38.93   $38.95   $38.90  
  Purchase #3 $151.89   8.440%   $164.7095   $164.71   $164.70   $164.70  
  Purchase #4 $222.31   5.427%   $234.3748   $234.37   $234.35   $234.40  
  Purchase #5 $217.48   11.370%   $242.2075   $242.21   $242.20   $242.20  
  Purchase #6 $160.38   9.285%   $175.2713   $175.27   $175.25   $175.30  
  Purchase #7 $186.70   5.541%   $197.045   $197.05   $197.05   $197.00  
  7 purchase totals = $1,095.83       $1,186.9068   $1,186.91   $1,186.85   $1,186.90