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 $46.97   10.831%   $52.0573   $52.06   $52.05   $52.10  
  Purchase #2 $64.82   12.523%   $72.9374   $72.94   $72.95   $72.90  
  Purchase #3 $114.81   5.803%   $121.4724   $121.47   $121.45   $121.50  
  Purchase #4 $151.60   8.242%   $164.0949   $164.09   $164.10   $164.10  
  Purchase #5 $144.90   12.553%   $163.0893   $163.09   $163.10   $163.10  
  Purchase #6 $190.83   4.111%   $198.675   $198.68   $198.70   $198.70  
  Purchase #7 $246.72   4.559%   $257.968   $257.97   $257.95   $258.00  
  7 purchase totals = $960.65       $1,030.2943   $1,030.30   $1,030.30   $1,030.40