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 $114.86   8.620%   $124.7609   $124.76   $124.75   $124.80  
  Purchase #2 $212.89   5.543%   $224.6905   $224.69   $224.70   $224.70  
  Purchase #3 $52.68   12.689%   $59.3646   $59.36   $59.35   $59.40  
  Purchase #4 $86.92   6.739%   $92.7775   $92.78   $92.80   $92.80  
  Purchase #5 $13.69   7.241%   $14.6813   $14.68   $14.70   $14.70  
  Purchase #6 $110.60   12.329%   $124.2359   $124.24   $124.25   $124.20  
  Purchase #7 $79.38   5.855%   $84.0277   $84.03   $84.05   $84.00  
  7 purchase totals = $671.02       $724.5384   $724.54   $724.60   $724.60