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 $85.75   12.197%   $96.2089   $96.21   $96.20   $96.20  
  Purchase #2 $241.93   9.730%   $265.4698   $265.47   $265.45   $265.50  
  Purchase #3 $207.86   11.532%   $231.8304   $231.83   $231.85   $231.80  
  Purchase #4 $214.82   6.639%   $229.0819   $229.08   $229.10   $229.10  
  Purchase #5 $73.65   6.843%   $78.6899   $78.69   $78.70   $78.70  
  Purchase #6 $111.41   7.558%   $119.8304   $119.83   $119.85   $119.80  
  Purchase #7 $53.58   8.138%   $57.9403   $57.94   $57.95   $57.90  
  7 purchase totals = $989.00       $1,079.0516   $1,079.05   $1,079.10   $1,079.00