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 $204.94   3.778%   $212.6826   $212.68   $212.70   $212.70  
  Purchase #2 $126.60   7.186%   $135.6975   $135.70   $135.70   $135.70  
  Purchase #3 $5.33   8.143%   $5.764   $5.76   $5.75   $5.80  
  Purchase #4 $70.63   9.723%   $77.4974   $77.50   $77.50   $77.50  
  Purchase #5 $49.90   12.691%   $56.2328   $56.23   $56.25   $56.20  
  Purchase #6 $206.55   7.393%   $221.8202   $221.82   $221.80   $221.80  
  Purchase #7 $83.44   3.744%   $86.564   $86.56   $86.55   $86.60  
  7 purchase totals = $747.39       $796.2585   $796.25   $796.25   $796.30