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 $69.56   10.247%   $76.6878   $76.69   $76.70   $76.70  
  Purchase #2 $239.92   6.838%   $256.3257   $256.33   $256.35   $256.30  
  Purchase #3 $180.77   11.399%   $201.376   $201.38   $201.40   $201.40  
  Purchase #4 $68.79   11.104%   $76.4284   $76.43   $76.45   $76.40  
  Purchase #5 $209.35   9.162%   $228.5306   $228.53   $228.55   $228.50  
  Purchase #6 $24.57   8.298%   $26.6088   $26.61   $26.60   $26.60  
  Purchase #7 $74.39   9.472%   $81.4362   $81.44   $81.45   $81.40  
  7 purchase totals = $867.35       $947.3935   $947.41   $947.50   $947.30