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 $129.99   3.355%   $134.3512   $134.35   $134.35   $134.40  
  Purchase #2 $149.91   4.336%   $156.4101   $156.41   $156.40   $156.40  
  Purchase #3 $7.96   4.433%   $8.3129   $8.31   $8.30   $8.30  
  Purchase #4 $185.25   12.661%   $208.7045   $208.70   $208.70   $208.70  
  Purchase #5 $249.36   10.418%   $275.3383   $275.34   $275.35   $275.30  
  Purchase #6 $70.62   10.293%   $77.8889   $77.89   $77.90   $77.90  
  Purchase #7 $241.88   8.251%   $261.8375   $261.84   $261.85   $261.80  
  7 purchase totals = $1,034.97       $1,122.8434   $1,122.84   $1,122.85   $1,122.80