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 $164.67   8.746%   $179.072   $179.07   $179.05   $179.10  
  Purchase #2 $78.91   5.481%   $83.2351   $83.24   $83.25   $83.20  
  Purchase #3 $127.55   8.486%   $138.3739   $138.37   $138.35   $138.40  
  Purchase #4 $174.64   4.554%   $182.5931   $182.59   $182.60   $182.60  
  Purchase #5 $250.60   9.164%   $273.565   $273.57   $273.55   $273.60  
  Purchase #6 $18.82   12.641%   $21.199   $21.20   $21.20   $21.20  
  Purchase #7 $80.25   3.109%   $82.745   $82.75   $82.75   $82.70  
  7 purchase totals = $895.44       $960.7831   $960.79   $960.75   $960.80