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 $54.83   8.644%   $59.5695   $59.57   $59.55   $59.60  
  Purchase #2 $129.95   12.359%   $146.0105   $146.01   $146.00   $146.00  
  Purchase #3 $69.89   9.570%   $76.5785   $76.58   $76.60   $76.60  
  Purchase #4 $85.43   8.451%   $92.6497   $92.65   $92.65   $92.60  
  Purchase #5 $224.70   10.721%   $248.7901   $248.79   $248.80   $248.80  
  Purchase #6 $135.27   13.702%   $153.8047   $153.80   $153.80   $153.80  
  Purchase #7 $68.78   11.635%   $76.7826   $76.78   $76.80   $76.80  
  7 purchase totals = $768.85       $854.1856   $854.18   $854.20   $854.20