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 $136.32   12.749%   $153.6994   $153.70   $153.70   $153.70  
  Purchase #2 $109.26   7.783%   $117.7637   $117.76   $117.75   $117.80  
  Purchase #3 $250.91   7.233%   $269.0583   $269.06   $269.05   $269.10  
  Purchase #4 $32.47   13.430%   $36.8307   $36.83   $36.85   $36.80  
  Purchase #5 $245.68   8.699%   $267.0517   $267.05   $267.05   $267.10  
  Purchase #6 $37.35   3.365%   $38.6068   $38.61   $38.60   $38.60  
  Purchase #7 $167.90   9.735%   $184.2451   $184.25   $184.25   $184.20  
  7 purchase totals = $979.89       $1,067.2557   $1,067.26   $1,067.25   $1,067.30