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 $163.53   12.863%   $184.5649   $184.56   $184.55   $184.60  
  Purchase #2 $167.28   8.239%   $181.0622   $181.06   $181.05   $181.10  
  Purchase #3 $234.76   7.592%   $252.583   $252.58   $252.60   $252.60  
  Purchase #4 $237.47   10.309%   $261.9508   $261.95   $261.95   $262.00  
  Purchase #5 $247.59   7.317%   $265.7062   $265.71   $265.70   $265.70  
  Purchase #6 $54.42   13.738%   $61.8962   $61.90   $61.90   $61.90  
  Purchase #7 $135.31   5.851%   $143.227   $143.23   $143.25   $143.20  
  7 purchase totals = $1,240.36       $1,350.9903   $1,350.99   $1,351.00   $1,351.10