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 $127.30   13.556%   $144.5568   $144.56   $144.55   $144.60  
  Purchase #2 $76.25   11.409%   $84.9494   $84.95   $84.95   $84.90  
  Purchase #3 $24.32   6.874%   $25.9918   $25.99   $26.00   $26.00  
  Purchase #4 $221.89   9.166%   $242.2284   $242.23   $242.25   $242.20  
  Purchase #5 $59.35   12.157%   $66.5652   $66.57   $66.55   $66.60  
  Purchase #6 $217.83   3.694%   $225.8766   $225.88   $225.90   $225.90  
  Purchase #7 $216.82   8.629%   $235.5294   $235.53   $235.55   $235.50  
  7 purchase totals = $943.76       $1,025.6976   $1,025.71   $1,025.75   $1,025.70