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 $185.71   11.439%   $206.9534   $206.95   $206.95   $207.00  
  Purchase #2 $5.77   13.250%   $6.5345   $6.53   $6.55   $6.50  
  Purchase #3 $180.88   11.182%   $201.106   $201.11   $201.10   $201.10  
  Purchase #4 $88.87   10.187%   $97.9232   $97.92   $97.90   $97.90  
  Purchase #5 $220.63   12.228%   $247.6086   $247.61   $247.60   $247.60  
  Purchase #6 $131.50   4.254%   $137.094   $137.09   $137.10   $137.10  
  Purchase #7 $66.45   4.223%   $69.2562   $69.26   $69.25   $69.30  
  7 purchase totals = $879.81       $966.4759   $966.47   $966.45   $966.50