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 $91.79   4.688%   $96.0931   $96.09   $96.10   $96.10  
  Purchase #2 $175.34   6.255%   $186.3075   $186.31   $186.30   $186.30  
  Purchase #3 $236.85   10.338%   $261.3356   $261.34   $261.35   $261.30  
  Purchase #4 $187.32   10.276%   $206.569   $206.57   $206.55   $206.60  
  Purchase #5 $66.89   7.489%   $71.8994   $71.90   $71.90   $71.90  
  Purchase #6 $134.65   6.669%   $143.6298   $143.63   $143.65   $143.60  
  Purchase #7 $70.65   11.585%   $78.8348   $78.83   $78.85   $78.80  
  7 purchase totals = $963.49       $1,044.6692   $1,044.67   $1,044.70   $1,044.60