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 $71.55   7.177%   $76.6851   $76.69   $76.70   $76.70  
  Purchase #2 $241.84   7.447%   $259.8498   $259.85   $259.85   $259.80  
  Purchase #3 $12.83   10.584%   $14.1879   $14.19   $14.20   $14.20  
  Purchase #4 $179.28   7.623%   $192.9465   $192.95   $192.95   $192.90  
  Purchase #5 $250.32   10.234%   $275.9377   $275.94   $275.95   $275.90  
  Purchase #6 $67.61   13.793%   $76.9354   $76.94   $76.95   $76.90  
  Purchase #7 $95.59   13.494%   $108.4889   $108.49   $108.50   $108.50  
  7 purchase totals = $919.02       $1,005.0313   $1,005.05   $1,005.10   $1,004.90