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 $238.48   5.726%   $252.1354   $252.14   $252.15   $252.10  
  Purchase #2 $174.56   9.333%   $190.8517   $190.85   $190.85   $190.90  
  Purchase #3 $164.88   7.863%   $177.8445   $177.84   $177.85   $177.80  
  Purchase #4 $143.97   7.345%   $154.5446   $154.54   $154.55   $154.50  
  Purchase #5 $197.61   5.708%   $208.8896   $208.89   $208.90   $208.90  
  Purchase #6 $27.43   3.519%   $28.3953   $28.40   $28.40   $28.40  
  Purchase #7 $10.44   6.345%   $11.1024   $11.10   $11.10   $11.10  
  7 purchase totals = $957.37       $1,023.7635   $1,023.76   $1,023.80   $1,023.70