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 $209.58   13.373%   $237.6071   $237.61   $237.60   $237.60  
  Purchase #2 $35.28   4.174%   $36.7526   $36.75   $36.75   $36.80  
  Purchase #3 $50.97   3.866%   $52.9405   $52.94   $52.95   $52.90  
  Purchase #4 $193.73   7.329%   $207.9285   $207.93   $207.95   $207.90  
  Purchase #5 $77.91   12.527%   $87.6698   $87.67   $87.65   $87.70  
  Purchase #6 $229.66   12.301%   $257.9105   $257.91   $257.90   $257.90  
  Purchase #7 $148.57   12.328%   $166.8857   $166.89   $166.90   $166.90  
  7 purchase totals = $945.70       $1,047.6947   $1,047.70   $1,047.70   $1,047.70