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 $41.42   5.338%   $43.631   $43.63   $43.65   $43.60  
  Purchase #2 $39.30   7.642%   $42.3033   $42.30   $42.30   $42.30  
  Purchase #3 $235.58   5.456%   $248.4332   $248.43   $248.45   $248.40  
  Purchase #4 $112.46   5.263%   $118.3788   $118.38   $118.40   $118.40  
  Purchase #5 $117.43   6.732%   $125.3354   $125.34   $125.35   $125.30  
  Purchase #6 $224.56   12.334%   $252.2572   $252.26   $252.25   $252.30  
  Purchase #7 $81.72   8.496%   $88.6629   $88.66   $88.65   $88.70  
  7 purchase totals = $852.47       $919.0018   $919.00   $919.05   $919.00