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 $24.62   5.719%   $26.028   $26.03   $26.05   $26.00  
  Purchase #2 $29.47   7.286%   $31.6172   $31.62   $31.60   $31.60  
  Purchase #3 $234.36   3.536%   $242.647   $242.65   $242.65   $242.60  
  Purchase #4 $77.81   8.758%   $84.6246   $84.62   $84.60   $84.60  
  Purchase #5 $23.73   7.605%   $25.5347   $25.53   $25.55   $25.50  
  Purchase #6 $87.93   8.292%   $95.2212   $95.22   $95.20   $95.20  
  Purchase #7 $102.89   13.323%   $116.598   $116.60   $116.60   $116.60  
  7 purchase totals = $580.81       $622.2707   $622.27   $622.25   $622.10