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 $205.93   5.696%   $217.6598   $217.66   $217.65   $217.70  
  Purchase #2 $5.68   3.632%   $5.8863   $5.89   $5.90   $5.90  
  Purchase #3 $200.56   10.444%   $221.5065   $221.51   $221.50   $221.50  
  Purchase #4 $73.61   9.522%   $80.6191   $80.62   $80.60   $80.60  
  Purchase #5 $238.25   10.854%   $264.1097   $264.11   $264.10   $264.10  
  Purchase #6 $151.58   8.115%   $163.8807   $163.88   $163.90   $163.90  
  Purchase #7 $60.59   11.794%   $67.736   $67.74   $67.75   $67.70  
  7 purchase totals = $936.20       $1,021.3981   $1,021.41   $1,021.40   $1,021.40