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 $69.94   11.179%   $77.7586   $77.76   $77.75   $77.80  
  Purchase #2 $192.66   11.328%   $214.4845   $214.48   $214.50   $214.50  
  Purchase #3 $247.94   9.281%   $270.9513   $270.95   $270.95   $271.00  
  Purchase #4 $154.56   4.850%   $162.0562   $162.06   $162.05   $162.10  
  Purchase #5 $81.86   12.103%   $91.7675   $91.77   $91.75   $91.80  
  Purchase #6 $170.68   9.298%   $186.5498   $186.55   $186.55   $186.50  
  Purchase #7 $59.75   6.749%   $63.7825   $63.78   $63.80   $63.80  
  7 purchase totals = $977.39       $1,067.3504   $1,067.35   $1,067.35   $1,067.50