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 $55.88   13.192%   $63.2517   $63.25   $63.25   $63.30  
  Purchase #2 $240.94   5.536%   $254.2784   $254.28   $254.30   $254.30  
  Purchase #3 $58.83   5.554%   $62.0974   $62.10   $62.10   $62.10  
  Purchase #4 $233.93   5.613%   $247.0605   $247.06   $247.05   $247.10  
  Purchase #5 $118.69   11.154%   $131.9287   $131.93   $131.95   $131.90  
  Purchase #6 $97.70   11.203%   $108.6453   $108.65   $108.65   $108.60  
  Purchase #7 $49.28   6.720%   $52.5916   $52.59   $52.60   $52.60  
  7 purchase totals = $855.25       $919.8536   $919.86   $919.90   $919.90