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 $144.93   6.673%   $154.6012   $154.60   $154.60   $154.60  
  Purchase #2 $128.45   10.292%   $141.6701   $141.67   $141.65   $141.70  
  Purchase #3 $238.49   9.587%   $261.354   $261.35   $261.35   $261.40  
  Purchase #4 $226.48   11.828%   $253.2681   $253.27   $253.25   $253.30  
  Purchase #5 $33.56   4.292%   $35.0004   $35.00   $35.00   $35.00  
  Purchase #6 $87.83   4.631%   $91.8974   $91.90   $91.90   $91.90  
  Purchase #7 $216.44   4.189%   $225.5067   $225.51   $225.50   $225.50  
  7 purchase totals = $1,076.18       $1,163.2979   $1,163.30   $1,163.25   $1,163.40