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 $217.85   8.426%   $236.206   $236.21   $236.20   $236.20  
  Purchase #2 $18.58   3.123%   $19.1603   $19.16   $19.15   $19.20  
  Purchase #3 $227.27   8.105%   $245.6902   $245.69   $245.70   $245.70  
  Purchase #4 $30.60   6.183%   $32.492   $32.49   $32.50   $32.50  
  Purchase #5 $126.83   11.357%   $141.2341   $141.23   $141.25   $141.20  
  Purchase #6 $236.83   8.224%   $256.3069   $256.31   $256.30   $256.30  
  Purchase #7 $72.25   3.204%   $74.5649   $74.56   $74.55   $74.60  
  7 purchase totals = $930.21       $1,005.6544   $1,005.65   $1,005.65   $1,005.70