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 $56.42   12.874%   $63.6835   $63.68   $63.70   $63.70  
  Purchase #2 $217.42   10.254%   $239.7142   $239.71   $239.70   $239.70  
  Purchase #3 $108.45   10.150%   $119.4577   $119.46   $119.45   $119.50  
  Purchase #4 $52.78   5.521%   $55.694   $55.69   $55.70   $55.70  
  Purchase #5 $159.71   4.756%   $167.3058   $167.31   $167.30   $167.30  
  Purchase #6 $66.79   4.247%   $69.6266   $69.63   $69.65   $69.60  
  Purchase #7 $249.81   10.793%   $276.772   $276.77   $276.75   $276.80  
  7 purchase totals = $911.38       $992.2538   $992.25   $992.25   $992.30