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 $49.82   10.704%   $55.1527   $55.15   $55.15   $55.20  
  Purchase #2 $40.49   8.703%   $44.0138   $44.01   $44.00   $44.00  
  Purchase #3 $114.85   13.436%   $130.2812   $130.28   $130.30   $130.30  
  Purchase #4 $167.86   5.730%   $177.4784   $177.48   $177.50   $177.50  
  Purchase #5 $213.65   8.354%   $231.4983   $231.50   $231.50   $231.50  
  Purchase #6 $166.93   13.482%   $189.4355   $189.44   $189.45   $189.40  
  Purchase #7 $178.76   10.846%   $198.1483   $198.15   $198.15   $198.10  
  7 purchase totals = $932.36       $1,026.0082   $1,026.01   $1,026.05   $1,026.00