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 $150.87   8.639%   $163.9037   $163.90   $163.90   $163.90  
  Purchase #2 $117.76   5.197%   $123.88   $123.88   $123.90   $123.90  
  Purchase #3 $93.29   5.721%   $98.6271   $98.63   $98.65   $98.60  
  Purchase #4 $184.74   3.319%   $190.8715   $190.87   $190.85   $190.90  
  Purchase #5 $176.41   8.711%   $191.7771   $191.78   $191.80   $191.80  
  Purchase #6 $70.81   8.524%   $76.8458   $76.85   $76.85   $76.80  
  Purchase #7 $154.84   6.466%   $164.852   $164.85   $164.85   $164.90  
  7 purchase totals = $948.72       $1,010.7572   $1,010.76   $1,010.80   $1,010.80