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 $58.70   11.679%   $65.5556   $65.56   $65.55   $65.60  
  Purchase #2 $61.77   12.829%   $69.6945   $69.69   $69.70   $69.70  
  Purchase #3 $183.77   4.552%   $192.1352   $192.14   $192.15   $192.10  
  Purchase #4 $30.41   8.676%   $33.0484   $33.05   $33.05   $33.00  
  Purchase #5 $5.48   10.369%   $6.0482   $6.05   $6.05   $6.00  
  Purchase #6 $230.97   10.208%   $254.5474   $254.55   $254.55   $254.50  
  Purchase #7 $230.94   13.673%   $262.5164   $262.52   $262.50   $262.50  
  7 purchase totals = $802.04       $883.5457   $883.56   $883.55   $883.40