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 $96.89   8.217%   $104.8515   $104.85   $104.85   $104.90  
  Purchase #2 $213.85   7.582%   $230.0641   $230.06   $230.05   $230.10  
  Purchase #3 $111.70   6.766%   $119.2576   $119.26   $119.25   $119.30  
  Purchase #4 $183.53   5.492%   $193.6095   $193.61   $193.60   $193.60  
  Purchase #5 $236.77   10.730%   $262.1754   $262.18   $262.20   $262.20  
  Purchase #6 $242.67   7.455%   $260.761   $260.76   $260.75   $260.80  
  Purchase #7 $86.46   4.556%   $90.3991   $90.40   $90.40   $90.40  
  7 purchase totals = $1,171.87       $1,261.1182   $1,261.12   $1,261.10   $1,261.30