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 $161.54   13.326%   $183.0668   $183.07   $183.05   $183.10  
  Purchase #2 $222.93   7.593%   $239.8571   $239.86   $239.85   $239.90  
  Purchase #3 $19.42   3.295%   $20.0599   $20.06   $20.05   $20.10  
  Purchase #4 $203.66   11.700%   $227.4882   $227.49   $227.50   $227.50  
  Purchase #5 $165.66   5.800%   $175.2683   $175.27   $175.25   $175.30  
  Purchase #6 $15.66   8.696%   $17.0218   $17.02   $17.00   $17.00  
  Purchase #7 $208.47   12.285%   $234.0805   $234.08   $234.10   $234.10  
  7 purchase totals = $997.34       $1,096.8426   $1,096.85   $1,096.80   $1,097.00