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 $239.85   4.498%   $250.6385   $250.64   $250.65   $250.60  
  Purchase #2 $14.71   10.496%   $16.254   $16.25   $16.25   $16.30  
  Purchase #3 $104.77   9.638%   $114.8677   $114.87   $114.85   $114.90  
  Purchase #4 $161.70   12.163%   $181.3676   $181.37   $181.35   $181.40  
  Purchase #5 $216.33   11.434%   $241.0652   $241.07   $241.05   $241.10  
  Purchase #6 $34.50   11.730%   $38.5469   $38.55   $38.55   $38.50  
  Purchase #7 $175.38   8.400%   $190.1119   $190.11   $190.10   $190.10  
  7 purchase totals = $947.24       $1,032.8518   $1,032.86   $1,032.80   $1,032.90