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 $115.71   8.682%   $125.7559   $125.76   $125.75   $125.80  
  Purchase #2 $205.34   9.727%   $225.3134   $225.31   $225.30   $225.30  
  Purchase #3 $46.80   7.488%   $50.3044   $50.30   $50.30   $50.30  
  Purchase #4 $64.38   10.329%   $71.0298   $71.03   $71.05   $71.00  
  Purchase #5 $67.62   4.683%   $70.7866   $70.79   $70.80   $70.80  
  Purchase #6 $188.66   6.826%   $201.5379   $201.54   $201.55   $201.50  
  Purchase #7 $235.65   7.209%   $252.638   $252.64   $252.65   $252.60  
  7 purchase totals = $924.16       $997.3660   $997.37   $997.40   $997.30