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 $186.99   11.788%   $209.0324   $209.03   $209.05   $209.00  
  Purchase #2 $205.66   10.747%   $227.7623   $227.76   $227.75   $227.80  
  Purchase #3 $71.59   6.811%   $76.466   $76.47   $76.45   $76.50  
  Purchase #4 $158.88   3.138%   $163.8657   $163.87   $163.85   $163.90  
  Purchase #5 $56.50   9.649%   $61.9517   $61.95   $61.95   $62.00  
  Purchase #6 $183.46   4.667%   $192.0221   $192.02   $192.00   $192.00  
  Purchase #7 $125.25   4.594%   $131.004   $131.00   $131.00   $131.00  
  7 purchase totals = $988.33       $1,062.1042   $1,062.10   $1,062.05   $1,062.20