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 $243.82   7.346%   $261.731   $261.73   $261.75   $261.70  
  Purchase #2 $148.54   6.185%   $157.7272   $157.73   $157.75   $157.70  
  Purchase #3 $205.48   6.295%   $218.415   $218.42   $218.40   $218.40  
  Purchase #4 $8.88   4.166%   $9.2499   $9.25   $9.25   $9.20  
  Purchase #5 $157.58   12.166%   $176.7512   $176.75   $176.75   $176.80  
  Purchase #6 $168.81   10.186%   $186.005   $186.01   $186.00   $186.00  
  Purchase #7 $225.89   4.478%   $236.0054   $236.01   $236.00   $236.00  
  7 purchase totals = $1,159.00       $1,245.8847   $1,245.90   $1,245.90   $1,245.80