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 $85.78   10.344%   $94.6531   $94.65   $94.65   $94.70  
  Purchase #2 $75.38   11.705%   $84.2032   $84.20   $84.20   $84.20  
  Purchase #3 $87.80   12.622%   $98.8821   $98.88   $98.90   $98.90  
  Purchase #4 $248.53   3.643%   $257.5839   $257.58   $257.60   $257.60  
  Purchase #5 $123.58   3.523%   $127.9337   $127.93   $127.95   $127.90  
  Purchase #6 $65.67   3.565%   $68.0111   $68.01   $68.00   $68.00  
  Purchase #7 $224.30   7.725%   $241.6272   $241.63   $241.65   $241.60  
  7 purchase totals = $911.04       $972.8943   $972.88   $972.95   $972.90