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 $171.32   8.662%   $186.1597   $186.16   $186.15   $186.20  
  Purchase #2 $107.51   11.302%   $119.6608   $119.66   $119.65   $119.70  
  Purchase #3 $109.70   13.234%   $124.2177   $124.22   $124.20   $124.20  
  Purchase #4 $33.62   4.351%   $35.0828   $35.08   $35.10   $35.10  
  Purchase #5 $47.93   4.121%   $49.9052   $49.91   $49.90   $49.90  
  Purchase #6 $12.90   11.571%   $14.3927   $14.39   $14.40   $14.40  
  Purchase #7 $183.93   12.715%   $207.3167   $207.32   $207.30   $207.30  
  7 purchase totals = $666.91       $736.7356   $736.74   $736.70   $736.80