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 $190.57   8.118%   $206.0405   $206.04   $206.05   $206.00  
  Purchase #2 $161.36   12.530%   $181.5784   $181.58   $181.60   $181.60  
  Purchase #3 $11.65   4.346%   $12.1563   $12.16   $12.15   $12.20  
  Purchase #4 $238.57   8.622%   $259.1395   $259.14   $259.15   $259.10  
  Purchase #5 $207.36   13.147%   $234.6216   $234.62   $234.60   $234.60  
  Purchase #6 $10.34   11.272%   $11.5055   $11.51   $11.50   $11.50  
  Purchase #7 $52.84   10.699%   $58.4934   $58.49   $58.50   $58.50  
  7 purchase totals = $872.69       $963.5352   $963.54   $963.55   $963.50