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 $65.61   8.846%   $71.4139   $71.41   $71.40   $71.40  
  Purchase #2 $229.43   13.220%   $259.7606   $259.76   $259.75   $259.80  
  Purchase #3 $247.56   12.170%   $277.6881   $277.69   $277.70   $277.70  
  Purchase #4 $250.65   8.786%   $272.6721   $272.67   $272.65   $272.70  
  Purchase #5 $237.33   7.568%   $255.2911   $255.29   $255.30   $255.30  
  Purchase #6 $238.47   9.692%   $261.5825   $261.58   $261.60   $261.60  
  Purchase #7 $53.66   10.396%   $59.2385   $59.24   $59.25   $59.20  
  7 purchase totals = $1,322.71       $1,457.6468   $1,457.64   $1,457.65   $1,457.70