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 $14.58   4.719%   $15.268   $15.27   $15.25   $15.30  
  Purchase #2 $26.88   11.793%   $30.05   $30.05   $30.05   $30.10  
  Purchase #3 $88.63   7.372%   $95.1638   $95.16   $95.15   $95.20  
  Purchase #4 $206.92   12.354%   $232.4829   $232.48   $232.50   $232.50  
  Purchase #5 $92.49   9.613%   $101.3811   $101.38   $101.40   $101.40  
  Purchase #6 $207.39   10.212%   $228.5687   $228.57   $228.55   $228.60  
  Purchase #7 $223.50   7.647%   $240.591   $240.59   $240.60   $240.60  
  7 purchase totals = $860.39       $943.5055   $943.50   $943.50   $943.70