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 $14.55   13.761%   $16.5522   $16.55   $16.55   $16.60  
  Purchase #2 $98.57   7.190%   $105.6572   $105.66   $105.65   $105.70  
  Purchase #3 $237.92   10.451%   $262.785   $262.79   $262.80   $262.80  
  Purchase #4 $176.49   10.858%   $195.6533   $195.65   $195.65   $195.70  
  Purchase #5 $97.72   11.573%   $109.0291   $109.03   $109.05   $109.00  
  Purchase #6 $182.68   12.621%   $205.736   $205.74   $205.75   $205.70  
  Purchase #7 $22.38   8.479%   $24.2776   $24.28   $24.30   $24.30  
  7 purchase totals = $830.31       $919.6904   $919.70   $919.75   $919.80