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 $56.49   8.514%   $61.2996   $61.30   $61.30   $61.30  
  Purchase #2 $146.67   11.459%   $163.4769   $163.48   $163.50   $163.50  
  Purchase #3 $193.60   4.275%   $201.8764   $201.88   $201.90   $201.90  
  Purchase #4 $52.83   6.482%   $56.2544   $56.25   $56.25   $56.30  
  Purchase #5 $210.66   9.380%   $230.4199   $230.42   $230.40   $230.40  
  Purchase #6 $190.31   6.484%   $202.6497   $202.65   $202.65   $202.60  
  Purchase #7 $38.86   3.678%   $40.2893   $40.29   $40.30   $40.30  
  7 purchase totals = $889.42       $956.2662   $956.27   $956.30   $956.30