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 $182.32   11.761%   $203.7627   $203.76   $203.75   $203.80  
  Purchase #2 $6.37   6.126%   $6.7602   $6.76   $6.75   $6.80  
  Purchase #3 $190.33   9.572%   $208.5484   $208.55   $208.55   $208.50  
  Purchase #4 $225.83   7.589%   $242.9682   $242.97   $242.95   $243.00  
  Purchase #5 $227.37   8.601%   $246.9261   $246.93   $246.95   $246.90  
  Purchase #6 $73.70   6.724%   $78.6556   $78.66   $78.65   $78.70  
  Purchase #7 $236.25   7.805%   $254.6893   $254.69   $254.70   $254.70  
  7 purchase totals = $1,142.17       $1,242.3105   $1,242.32   $1,242.30   $1,242.40