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 $104.53   9.623%   $114.5889   $114.59   $114.60   $114.60  
  Purchase #2 $221.80   8.121%   $239.8124   $239.81   $239.80   $239.80  
  Purchase #3 $132.93   4.331%   $138.6872   $138.69   $138.70   $138.70  
  Purchase #4 $17.63   7.624%   $18.9741   $18.97   $18.95   $19.00  
  Purchase #5 $59.42   9.113%   $64.8349   $64.83   $64.85   $64.80  
  Purchase #6 $133.66   4.280%   $139.3806   $139.38   $139.40   $139.40  
  Purchase #7 $214.90   7.343%   $230.6801   $230.68   $230.70   $230.70  
  7 purchase totals = $884.87       $946.9582   $946.95   $947.00   $947.00