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 $24.49   8.445%   $26.5582   $26.56   $26.55   $26.60  
  Purchase #2 $214.39   9.269%   $234.2618   $234.26   $234.25   $234.30  
  Purchase #3 $119.81   12.351%   $134.6077   $134.61   $134.60   $134.60  
  Purchase #4 $22.94   3.152%   $23.6631   $23.66   $23.65   $23.70  
  Purchase #5 $235.70   10.279%   $259.9276   $259.93   $259.95   $259.90  
  Purchase #6 $88.70   3.253%   $91.5854   $91.59   $91.60   $91.60  
  Purchase #7 $13.60   3.301%   $14.0489   $14.05   $14.05   $14.00  
  7 purchase totals = $719.63       $784.6527   $784.66   $784.65   $784.70