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 $242.88   10.655%   $268.7589   $268.76   $268.75   $268.80  
  Purchase #2 $67.45   8.835%   $73.4092   $73.41   $73.40   $73.40  
  Purchase #3 $203.38   10.624%   $224.9871   $224.99   $225.00   $225.00  
  Purchase #4 $43.79   13.521%   $49.7108   $49.71   $49.70   $49.70  
  Purchase #5 $57.66   4.730%   $60.3873   $60.39   $60.40   $60.40  
  Purchase #6 $62.48   9.766%   $68.5818   $68.58   $68.60   $68.60  
  Purchase #7 $156.28   4.366%   $163.1032   $163.10   $163.10   $163.10  
  7 purchase totals = $833.92       $908.9383   $908.94   $908.95   $909.00