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 $188.85   9.510%   $206.8096   $206.81   $206.80   $206.80  
  Purchase #2 $114.41   11.756%   $127.86   $127.86   $127.85   $127.90  
  Purchase #3 $68.46   6.198%   $72.7032   $72.70   $72.70   $72.70  
  Purchase #4 $180.74   11.542%   $201.601   $201.60   $201.60   $201.60  
  Purchase #5 $129.62   7.446%   $139.2715   $139.27   $139.25   $139.30  
  Purchase #6 $117.74   13.478%   $133.609   $133.61   $133.60   $133.60  
  Purchase #7 $235.44   10.859%   $261.0064   $261.01   $261.00   $261.00  
  7 purchase totals = $1,035.26       $1,142.8607   $1,142.86   $1,142.80   $1,142.90