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 $78.32   5.423%   $82.5673   $82.57   $82.55   $82.60  
  Purchase #2 $248.33   4.167%   $258.6779   $258.68   $258.70   $258.70  
  Purchase #3 $152.90   11.211%   $170.0416   $170.04   $170.05   $170.00  
  Purchase #4 $189.71   12.672%   $213.7501   $213.75   $213.75   $213.80  
  Purchase #5 $140.57   12.321%   $157.8896   $157.89   $157.90   $157.90  
  Purchase #6 $199.87   5.701%   $211.2646   $211.26   $211.25   $211.30  
  Purchase #7 $242.94   7.613%   $261.435   $261.44   $261.45   $261.40  
  7 purchase totals = $1,252.64       $1,355.6261   $1,355.63   $1,355.65   $1,355.70