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 $232.66   6.787%   $248.4506   $248.45   $248.45   $248.50  
  Purchase #2 $195.75   5.487%   $206.4908   $206.49   $206.50   $206.50  
  Purchase #3 $16.61   8.575%   $18.0343   $18.03   $18.05   $18.00  
  Purchase #4 $113.27   3.526%   $117.2639   $117.26   $117.25   $117.30  
  Purchase #5 $212.88   12.387%   $239.2494   $239.25   $239.25   $239.20  
  Purchase #6 $192.41   10.755%   $213.1037   $213.10   $213.10   $213.10  
  Purchase #7 $139.47   8.175%   $150.8717   $150.87   $150.85   $150.90  
  7 purchase totals = $1,103.05       $1,193.4644   $1,193.45   $1,193.45   $1,193.50