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 $76.41   11.126%   $84.9114   $84.91   $84.90   $84.90  
  Purchase #2 $22.31   5.359%   $23.5056   $23.51   $23.50   $23.50  
  Purchase #3 $119.42   7.322%   $128.1639   $128.16   $128.15   $128.20  
  Purchase #4 $58.47   5.287%   $61.5613   $61.56   $61.55   $61.60  
  Purchase #5 $13.76   6.355%   $14.6344   $14.63   $14.65   $14.60  
  Purchase #6 $112.50   13.530%   $127.7213   $127.72   $127.70   $127.70  
  Purchase #7 $58.99   7.788%   $63.5841   $63.58   $63.60   $63.60  
  7 purchase totals = $461.86       $504.0820   $504.07   $504.05   $504.10