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 $246.44   6.383%   $262.1703   $262.17   $262.15   $262.20  
  Purchase #2 $113.59   9.579%   $124.4708   $124.47   $124.45   $124.50  
  Purchase #3 $238.85   9.564%   $261.6936   $261.69   $261.70   $261.70  
  Purchase #4 $220.88   7.481%   $237.404   $237.40   $237.40   $237.40  
  Purchase #5 $109.42   13.715%   $124.427   $124.43   $124.45   $124.40  
  Purchase #6 $75.38   6.350%   $80.1666   $80.17   $80.15   $80.20  
  Purchase #7 $63.70   5.615%   $67.2768   $67.28   $67.30   $67.30  
  7 purchase totals = $1,068.26       $1,157.6091   $1,157.61   $1,157.60   $1,157.70