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 $246.83   5.864%   $261.3041   $261.30   $261.30   $261.30  
  Purchase #2 $231.62   5.635%   $244.6718   $244.67   $244.65   $244.70  
  Purchase #3 $137.34   12.562%   $154.5927   $154.59   $154.60   $154.60  
  Purchase #4 $228.27   13.249%   $258.5135   $258.51   $258.50   $258.50  
  Purchase #5 $106.80   7.275%   $114.5697   $114.57   $114.55   $114.60  
  Purchase #6 $246.59   12.511%   $277.4409   $277.44   $277.45   $277.40  
  Purchase #7 $228.69   9.625%   $250.7014   $250.70   $250.70   $250.70  
  7 purchase totals = $1,426.14       $1,561.7941   $1,561.78   $1,561.75   $1,561.80