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 $248.67   4.392%   $259.5916   $259.59   $259.60   $259.60  
  Purchase #2 $48.90   13.357%   $55.4316   $55.43   $55.45   $55.40  
  Purchase #3 $241.99   12.211%   $271.5394   $271.54   $271.55   $271.50  
  Purchase #4 $194.63   9.636%   $213.3845   $213.38   $213.40   $213.40  
  Purchase #5 $168.41   6.850%   $179.9461   $179.95   $179.95   $179.90  
  Purchase #6 $60.76   12.138%   $68.135   $68.14   $68.15   $68.10  
  Purchase #7 $206.26   6.463%   $219.5906   $219.59   $219.60   $219.60  
  7 purchase totals = $1,169.62       $1,267.6188   $1,267.62   $1,267.70   $1,267.50