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 $30.77   8.364%   $33.3436   $33.34   $33.35   $33.30  
  Purchase #2 $126.47   11.194%   $140.6271   $140.63   $140.65   $140.60  
  Purchase #3 $201.54   9.855%   $221.4018   $221.40   $221.40   $221.40  
  Purchase #4 $161.31   8.483%   $174.9939   $174.99   $175.00   $175.00  
  Purchase #5 $237.70   10.215%   $261.9811   $261.98   $262.00   $262.00  
  Purchase #6 $119.38   9.385%   $130.5838   $130.58   $130.60   $130.60  
  Purchase #7 $68.75   10.592%   $76.032   $76.03   $76.05   $76.00  
  7 purchase totals = $945.92       $1,038.9633   $1,038.95   $1,039.05   $1,038.90