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 $242.86   7.660%   $261.4631   $261.46   $261.45   $261.50  
  Purchase #2 $114.31   10.616%   $126.4451   $126.45   $126.45   $126.40  
  Purchase #3 $166.29   4.831%   $174.3235   $174.32   $174.30   $174.30  
  Purchase #4 $137.41   7.472%   $147.6773   $147.68   $147.70   $147.70  
  Purchase #5 $132.40   5.240%   $139.3378   $139.34   $139.35   $139.30  
  Purchase #6 $85.62   5.611%   $90.4241   $90.42   $90.40   $90.40  
  Purchase #7 $15.91   13.185%   $18.0077   $18.01   $18.00   $18.00  
  7 purchase totals = $894.80       $957.6786   $957.68   $957.65   $957.60