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 $213.39   3.438%   $220.7263   $220.73   $220.75   $220.70  
  Purchase #2 $169.58   4.234%   $176.76   $176.76   $176.75   $176.80  
  Purchase #3 $61.39   3.723%   $63.6755   $63.68   $63.70   $63.70  
  Purchase #4 $207.27   9.797%   $227.5762   $227.58   $227.60   $227.60  
  Purchase #5 $107.86   4.245%   $112.4387   $112.44   $112.45   $112.40  
  Purchase #6 $56.38   12.316%   $63.3238   $63.32   $63.30   $63.30  
  Purchase #7 $32.44   8.191%   $35.0972   $35.10   $35.10   $35.10  
  7 purchase totals = $848.31       $899.5977   $899.61   $899.65   $899.60