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 $31.98   7.741%   $34.4556   $34.46   $34.45   $34.50  
  Purchase #2 $97.49   5.397%   $102.7515   $102.75   $102.75   $102.80  
  Purchase #3 $158.84   13.668%   $180.5503   $180.55   $180.55   $180.60  
  Purchase #4 $208.41   11.500%   $232.3772   $232.38   $232.40   $232.40  
  Purchase #5 $247.64   5.560%   $261.4088   $261.41   $261.40   $261.40  
  Purchase #6 $66.36   10.572%   $73.3756   $73.38   $73.40   $73.40  
  Purchase #7 $215.99   11.800%   $241.4768   $241.48   $241.50   $241.50  
  7 purchase totals = $1,026.71       $1,126.3958   $1,126.41   $1,126.45   $1,126.60