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 $71.48   11.203%   $79.4879   $79.49   $79.50   $79.50  
  Purchase #2 $232.54   12.367%   $261.2982   $261.30   $261.30   $261.30  
  Purchase #3 $204.74   9.744%   $224.6899   $224.69   $224.70   $224.70  
  Purchase #4 $42.35   8.795%   $46.0747   $46.07   $46.05   $46.10  
  Purchase #5 $226.73   8.833%   $246.7571   $246.76   $246.75   $246.80  
  Purchase #6 $182.29   4.710%   $190.8759   $190.88   $190.90   $190.90  
  Purchase #7 $231.94   4.736%   $242.9247   $242.92   $242.90   $242.90  
  7 purchase totals = $1,192.07       $1,292.1084   $1,292.11   $1,292.10   $1,292.20