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 $238.69   12.477%   $268.4714   $268.47   $268.45   $268.50  
  Purchase #2 $174.84   12.701%   $197.0464   $197.05   $197.05   $197.00  
  Purchase #3 $167.46   11.579%   $186.8502   $186.85   $186.85   $186.90  
  Purchase #4 $105.91   4.525%   $110.7024   $110.70   $110.70   $110.70  
  Purchase #5 $121.49   4.656%   $127.1466   $127.15   $127.15   $127.10  
  Purchase #6 $32.96   5.264%   $34.695   $34.70   $34.70   $34.70  
  Purchase #7 $57.30   8.291%   $62.0507   $62.05   $62.05   $62.10  
  7 purchase totals = $898.65       $986.9627   $986.97   $986.95   $987.00