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 $68.33   12.708%   $77.0134   $77.01   $77.00   $77.00  
  Purchase #2 $232.35   12.342%   $261.0266   $261.03   $261.05   $261.00  
  Purchase #3 $118.44   7.602%   $127.4438   $127.44   $127.45   $127.40  
  Purchase #4 $103.68   5.273%   $109.147   $109.15   $109.15   $109.10  
  Purchase #5 $156.62   8.174%   $169.4221   $169.42   $169.40   $169.40  
  Purchase #6 $37.77   12.606%   $42.5313   $42.53   $42.55   $42.50  
  Purchase #7 $228.50   5.807%   $241.769   $241.77   $241.75   $241.80  
  7 purchase totals = $945.69       $1,028.3532   $1,028.35   $1,028.35   $1,028.20