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 $94.69   10.813%   $104.9288   $104.93   $104.95   $104.90  
  Purchase #2 $162.84   7.874%   $175.662   $175.66   $175.65   $175.70  
  Purchase #3 $39.85   10.616%   $44.0805   $44.08   $44.10   $44.10  
  Purchase #4 $169.76   9.722%   $186.2641   $186.26   $186.25   $186.30  
  Purchase #5 $222.29   8.733%   $241.7026   $241.70   $241.70   $241.70  
  Purchase #6 $105.82   8.252%   $114.5523   $114.55   $114.55   $114.60  
  Purchase #7 $68.26   12.507%   $76.7973   $76.80   $76.80   $76.80  
  7 purchase totals = $863.51       $943.9876   $943.98   $944.00   $944.10