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 $55.86   8.277%   $60.4835   $60.48   $60.50   $60.50  
  Purchase #2 $53.93   13.320%   $61.1135   $61.11   $61.10   $61.10  
  Purchase #3 $174.58   5.631%   $184.4106   $184.41   $184.40   $184.40  
  Purchase #4 $171.82   8.350%   $186.167   $186.17   $186.15   $186.20  
  Purchase #5 $216.48   9.248%   $236.5001   $236.50   $236.50   $236.50  
  Purchase #6 $69.31   3.294%   $71.5931   $71.59   $71.60   $71.60  
  Purchase #7 $123.54   7.804%   $133.1811   $133.18   $133.20   $133.20  
  7 purchase totals = $865.52       $933.4489   $933.44   $933.45   $933.50