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 $126.93   12.696%   $143.045   $143.05   $143.05   $143.00  
  Purchase #2 $94.72   4.446%   $98.9313   $98.93   $98.95   $98.90  
  Purchase #3 $46.41   6.541%   $49.4457   $49.45   $49.45   $49.40  
  Purchase #4 $218.62   11.733%   $244.2707   $244.27   $244.25   $244.30  
  Purchase #5 $126.81   12.151%   $142.2187   $142.22   $142.20   $142.20  
  Purchase #6 $236.63   12.248%   $265.6124   $265.61   $265.60   $265.60  
  Purchase #7 $120.44   8.813%   $131.0544   $131.05   $131.05   $131.10  
  7 purchase totals = $970.56       $1,074.5782   $1,074.58   $1,074.55   $1,074.50