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 $168.94   6.341%   $179.6525   $179.65   $179.65   $179.70  
  Purchase #2 $135.95   6.324%   $144.5475   $144.55   $144.55   $144.50  
  Purchase #3 $242.65   6.150%   $257.573   $257.57   $257.55   $257.60  
  Purchase #4 $242.45   11.621%   $270.6251   $270.63   $270.65   $270.60  
  Purchase #5 $43.57   6.730%   $46.5023   $46.50   $46.50   $46.50  
  Purchase #6 $224.38   4.375%   $234.1966   $234.20   $234.20   $234.20  
  Purchase #7 $73.50   4.208%   $76.5929   $76.59   $76.60   $76.60  
  7 purchase totals = $1,131.44       $1,209.6899   $1,209.69   $1,209.70   $1,209.70