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 $8.70   3.558%   $9.0095   $9.01   $9.00   $9.00  
  Purchase #2 $173.43   4.247%   $180.7956   $180.80   $180.80   $180.80  
  Purchase #3 $90.79   13.314%   $102.8778   $102.88   $102.90   $102.90  
  Purchase #4 $105.61   10.859%   $117.0782   $117.08   $117.10   $117.10  
  Purchase #5 $179.45   11.859%   $200.731   $200.73   $200.75   $200.70  
  Purchase #6 $184.86   3.123%   $190.6332   $190.63   $190.65   $190.60  
  Purchase #7 $206.97   10.105%   $227.8843   $227.88   $227.90   $227.90  
  7 purchase totals = $949.81       $1,029.0096   $1,029.01   $1,029.10   $1,029.00