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 $75.67   11.797%   $84.5968   $84.60   $84.60   $84.60  
  Purchase #2 $224.86   7.201%   $241.0522   $241.05   $241.05   $241.10  
  Purchase #3 $74.68   3.366%   $77.1937   $77.19   $77.20   $77.20  
  Purchase #4 $79.41   3.354%   $82.0734   $82.07   $82.05   $82.10  
  Purchase #5 $175.63   11.647%   $196.0856   $196.09   $196.10   $196.10  
  Purchase #6 $166.52   7.641%   $179.2438   $179.24   $179.25   $179.20  
  Purchase #7 $130.81   10.168%   $144.1108   $144.11   $144.10   $144.10  
  7 purchase totals = $927.58       $1,004.3563   $1,004.35   $1,004.35   $1,004.40