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 $239.97   5.775%   $253.8283   $253.83   $253.85   $253.80  
  Purchase #2 $48.98   7.410%   $52.6094   $52.61   $52.60   $52.60  
  Purchase #3 $155.60   6.731%   $166.0734   $166.07   $166.05   $166.10  
  Purchase #4 $118.47   12.816%   $133.6531   $133.65   $133.65   $133.70  
  Purchase #5 $64.75   12.443%   $72.8068   $72.81   $72.80   $72.80  
  Purchase #6 $175.85   7.870%   $189.6894   $189.69   $189.70   $189.70  
  Purchase #7 $144.31   7.215%   $154.722   $154.72   $154.70   $154.70  
  7 purchase totals = $947.93       $1,023.3824   $1,023.38   $1,023.35   $1,023.40