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 $241.63   8.130%   $261.2745   $261.27   $261.25   $261.30  
  Purchase #2 $173.58   10.127%   $191.1584   $191.16   $191.15   $191.20  
  Purchase #3 $124.59   12.579%   $140.2622   $140.26   $140.25   $140.30  
  Purchase #4 $113.57   11.848%   $127.0258   $127.03   $127.05   $127.00  
  Purchase #5 $181.78   5.175%   $191.1871   $191.19   $191.20   $191.20  
  Purchase #6 $53.93   5.555%   $56.9258   $56.93   $56.95   $56.90  
  Purchase #7 $41.61   7.657%   $44.7961   $44.80   $44.80   $44.80  
  7 purchase totals = $930.69       $1,012.6299   $1,012.64   $1,012.65   $1,012.70