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 $126.96   10.477%   $140.2616   $140.26   $140.25   $140.30  
  Purchase #2 $109.32   9.226%   $119.4059   $119.41   $119.40   $119.40  
  Purchase #3 $163.95   13.533%   $186.1374   $186.14   $186.15   $186.10  
  Purchase #4 $73.50   10.309%   $81.0771   $81.08   $81.10   $81.10  
  Purchase #5 $87.61   5.352%   $92.2989   $92.30   $92.30   $92.30  
  Purchase #6 $24.42   6.527%   $26.0139   $26.01   $26.00   $26.00  
  Purchase #7 $100.75   6.833%   $107.6342   $107.63   $107.65   $107.60  
  7 purchase totals = $686.51       $752.8290   $752.83   $752.85   $752.80