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 $249.73   4.554%   $261.1027   $261.10   $261.10   $261.10  
  Purchase #2 $88.65   12.525%   $99.7534   $99.75   $99.75   $99.80  
  Purchase #3 $49.52   13.280%   $56.0963   $56.10   $56.10   $56.10  
  Purchase #4 $173.41   4.212%   $180.714   $180.71   $180.70   $180.70  
  Purchase #5 $205.40   10.116%   $226.1783   $226.18   $226.20   $226.20  
  Purchase #6 $5.94   3.788%   $6.165   $6.17   $6.15   $6.20  
  Purchase #7 $182.89   9.771%   $200.7602   $200.76   $200.75   $200.80  
  7 purchase totals = $955.54       $1,030.7699   $1,030.77   $1,030.75   $1,030.90