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 $24.54   8.741%   $26.685   $26.69   $26.70   $26.70  
  Purchase #2 $117.31   6.279%   $124.6759   $124.68   $124.70   $124.70  
  Purchase #3 $18.88   7.396%   $20.2764   $20.28   $20.30   $20.30  
  Purchase #4 $178.70   13.705%   $203.1908   $203.19   $203.20   $203.20  
  Purchase #5 $78.39   13.852%   $89.2486   $89.25   $89.25   $89.20  
  Purchase #6 $105.78   12.558%   $119.0639   $119.06   $119.05   $119.10  
  Purchase #7 $180.33   11.745%   $201.5098   $201.51   $201.50   $201.50  
  7 purchase totals = $703.93       $784.6504   $784.66   $784.70   $784.70