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 $47.59   10.567%   $52.6188   $52.62   $52.60   $52.60  
  Purchase #2 $242.94   10.471%   $268.3782   $268.38   $268.40   $268.40  
  Purchase #3 $239.61   7.686%   $258.0264   $258.03   $258.05   $258.00  
  Purchase #4 $239.27   9.379%   $261.7111   $261.71   $261.70   $261.70  
  Purchase #5 $154.68   8.643%   $168.049   $168.05   $168.05   $168.00  
  Purchase #6 $60.56   7.660%   $65.1989   $65.20   $65.20   $65.20  
  Purchase #7 $203.64   11.140%   $226.3255   $226.33   $226.35   $226.30  
  7 purchase totals = $1,188.29       $1,300.3079   $1,300.32   $1,300.35   $1,300.20